1. Introduction: I am not the person that I am
It is conceivable that I was some other person than that which I currently am (viz. Edralis). In a different possible world, I could have not been Edralis, but, say, the person that is you, now reading this paper – I could have been now doing what you are doing, and have the body, personality, and memories that you have. I might have had a different body, a different personality, different memories, and still remain me in the sense that it would be me who experienced that body, personality, and memories, in the same way that I experience this body, this personality, have these memories now.
„I“ in this sense and the person that I am are conceptually distinguishable entities. I am not identical to the person that I am, or any person. That I am this particular person is not a tautology, but a contingent fact about how I am, and about how the world is. Me in this sense, that which could be and could have been some other person, is that which experiences, i.e. the subject of experience.
There are experiences which are mine, those which are present in the same way this experience that I am having now is present. The existence of this experience that I am having now is introspectively self-evident, and consists of many conceptually distinguishable parts –e.g. certain sounds, feelings, visual images etc., including those that make up my body– that however form a unity in that they are experienced simultaneously, i.e. in the same moment (which amounts to their being contiguous in a specific sense), and also by the same subject. They form a momentary perspective that I experience.
What momentary perspective –what phenomenal qualities, in what constellations– I experience changes with every moment. During these transformations of what is present, there is one thing that remains constant, even though those things which are present arise and cease to be: me, as the witness, the experiencer of these changes. I am the thisness that they fill, the subject, that which witnesses the change, relative to which the change happens: that is, the “frame” which the particular momentary perspective fills.
The existence of my experiences, including my body and memories, consists in them being present to me, as that which experiences them, for whom they are: like this particular experience, now, writing this. That which comes and goes is this particular this, and the subject is the thisness.
At different points in time, I am not myself in virtue of the content of my experiences, or their continuity. They are mine because I am what binds them together, regardless of whether there is any continuity present within them. My experiences include my body, emotions, and memories – therefore, these are not and do not constitute me as the subject that I am. Any and all of them could go and be replaced by different phenomena, but I would still persist, unchanged in myself, as long as there would be something, anything, for me – it might just be, say, an experience of a pulsing patch of red morphing into blue and back in a void without any memory of ever being some person, or just an unending experience of dread etc.
So that in virtue of which my experiences are all mine is not, in the sense relevant to my point, that they belong to some particular person (with a particular body, personality, memories). That they are mine means they are as this is, they are in the way that all these things here now are (the weight of the keyboard on my lap, the muted music from the fair outside, the whirling drone of the computer fan, the anxiety about that deadline); their existence consists in being present to me in the same way that those things that I experience now are present to me. 
The subject that I am is in itself devoid of any individuating characteristics of the kind that persons are usually imbued with and differentiated by: in itself, it has no personality, because personality consists of certain behavioral tendencies which translate to phenomena, and no feelings or memory, because, again, these are phenomena. To say that a subject has a body, or that a subject is some person, just means that there is an experience of a body (“one’s own body”), or a person, from the first person point of view, that is actualized in, or for that subject, not that that subject in itself has those things in the sense that it is constituted by them. A person may be reducible to these things, but a subject is not, even if they belong to it.
The only way the subject that I am is distinguished from any other subject, if there are any other subjects, is the fact that I am this subject. We are the same entity: I am the way this experience is present. Any experience that is present to this subject that is me is present in the way this current experience is present.
So that in virtue of which an experience is present in the way this experience (of writing this, now, in my room, cup of coffee at my elbow) is present is the subject that I am, regardless of what are the contents of that experience.
2. An analysis of phenomena: subject, phenomenal qualities, perspective
Phenomena can be analysed as consisting of a qualitative component and the subject of experience in which those qualities are actualized. Experiences come in distinct varieties, “feels” –in this paper, I will refer to this aspect of experience as phenomenal quality–, and they must also belong to some subject of experience.
Examples of phenomenal qualities include pain, redness, A440 pitch, the timbre of oboe, nostalgia, familiarity with some object, that feeling of apprehensive expectation, feeling of pressure and some particular texture on one’s fingertips, orgasm, coldness, greasiness, smell of chocolate, anxiety, dread, anger, hurt, the feeling of grasping the meaning of some concept or a sentence, the visual perception of some object, the visual image of some object in one’s imagination, self-consciousness, the feeling of a hypnagogic jerk, of peace, and saltiness.
Subject is that which experiences; that in (or, for) which phenomena are actualized, or in which phenomenal qualities, or perspectives, are actualized. Note that from “there is an experience” it follows that “there is a subject”. Phenomena (i.e. experiences) are “made out of” subjects presented with certain phenomenal qualities – an experience is just that, some phenomenal qualities actualized in some subject. Phenomenal qualities themselves are not phenomena: they constitute phenomena when they are actualized by being present to some subject.
A perspective is any constellation (momentary or temporally extended) of phenomenal qualities, but those that are actually expected to be actualized (to constitute some experience) are usually assumed to be centered around a person or some other living, encephalized being, a body of some kind, and have some sort of internal continuity. A perspective being centered simply means that there are certain regularly occurring or ubiquitous phenomenal qualities which resemble each other and form a continuity, for example a body seen from the first person point of view which serves as the center of the visual part of the perspective (and which is also considered the body of that particular person, and is associated with some unique phenomena, e.g. tactile experiences, which (normally) only occur “within” this body, or at its edges).
A perspective is actualized if it is present to some subject, i.e. if it constitutes some experience. The same perspective can be actualized many times, and in multiple subjects, i.e. it can have many (an infinite number of) actualizations. A perspective can also be only partially actualized, or its parts actualized in different subjects. An actualization of some perspective is a set of experiences which corresponds by its qualitative content to the entirety of that perspective (that is, unless it is only a partial actualization). For example, if perspective P includes phenomenal qualities x, y, z in constellation c, then if that perspective is actualized, there exists at least one actualization of that perspective, i.e. a set of experiences which consists of phenomenal qualities x, y, z in constellation c present to some subject.
Persons, as they are usually conceived, e.g. Edralis, correspond to some particular perspective, a person-perspective, about which it is usually assumed that it is actualized in some (one) subject: if that person is a zombie, that perspective is not actualized for that person; and if it is actualized, it can be actualized once or many times in part or in whole in one or multiple subjects. It is also conceivable that the same subject experiences the same perspective many times, i.e. that the perspective is actualized multiple times in a single subject.
For example, there is a perspective of the person E, which is the set of all momentary perespectives that are expected to be experienced by E during her lifetime, but as she is, at the time of writing this paper, still alive, it is so far only partially actualized, because there are, at the time of writing this paper, still parts of that perspective which have not yet been actualized in some subject, or at least that is what is usually assumed to be the case. It is also possible that until this morning, E was actually a zombie and her perspective gained a subject only some hours ago, and the experiences constituting her perspective until yesterday will never be actualized (even though it is conceivable that yesterday experiences are actualized after this moment now), in which case again, only a part of her perspective would really ever be actualized for her.
The sum of phenomenal qualities that are present to a subject at any particular moment constitutes its momentary perspective. The experience itself is then an actualization of that momentary perspective. The sum of all momentary perspectives of a particular subject make up the subject-perspective of that subject. The actualization of that perspective is the experiential whole pertaining to that subject, i.e. the sum of all its experiences. A particular subject-perspective is necessarily actualized at least once, in that particular subject, but theoretically it could be actualized in multiple subjects.
I know with certainty that the perspective which constitutes my current experience is being actualized in my subject – I witness it directly, my experience is that actualization. This momentary perspective, that which I experience now, which constitutes my current experience, is made out of phenomenal qualities in certain constellations which also constitute a slice of the perspective that corresponds to the person E, of which I am fairly certain I shall experience the entirety of (i.e. that all phenomenal qualities that make up her perspective will be present like this particular moment is present to me now), even though it might as well be the case I will not – there is no way for me to ascertain this; and it is also necessarily a slice of the subject-perspective of the subject that I am. This particular experience that I’m having now is an actualization of some part of E-perspective, apart from being an actualization of some part of the subject-perspective of the subject that I am.
So at least in this particular moment, now, the momentary part of my subject-perspective (i.e. my momentary perspective) is the same as some part of E-perspective: it is the case that in this present moment, writing this, the view I have “from the inside” belongs to a perspective of a person identified as E.
From the fact that there exists a E-perspective it doesn’t necessarily follow that this perspective is actualized in its entirety, and that it is me in whom it is actualized, even though at least some of my experiences happen to be actualizations of a part of E-perspective: it is conceivable that I will stop existing tonight, and tomorrow E-perspective will continue to be actualized in some other subject (or multiple subjects at once), or perhaps the perspective won’t be actualized any longer and E will become a zombie.
E’s experiences could have conceivably existed even if I, as the subject for which her perspective is live, did not. The experiences which she had and will have, and has in this particular moment, of writing this, might have been experienced by some other subject, even though that wouldn’t change anything about the fact that they would be hers, i.e. E’s.
E-perspective and my subject-perspective are momentarily aligned, i.e. they currently share content – that which constitutes my momentary experience. I know with absolute certainty I will experience the entirety of my subject-perspective (it is inconceivable that I do not), and only those momentary perspectives which are a part of this perspective, but I cannot know with certainty that I will experience the entirety of E-perspective, or that I will ever experience only those momentary perspectives which are part of E-perspective, and not also some other momentary perspectives, of some other person-perspectives, because it is conceivable that I do not. Because person-perspectives include memories, if I did experience other person-perspectives, I have no way of knowing this. And even if I did remember being some other person, that does not necessarily mean I was that person, i.e. that I actually experienced that which I remember.
3. Which experiences are mine? How many subjects are there?
There are other person-perspectives besides the E-perspective, corresponding to different people and other beings, and it is usually assumed that they are also actualized in some subject, and each of them in a different one, and none of them is me. That is, it is usually assumed there are views “from the inside” that are not my own, that there are other thisnesses; that there are other subjects, beside myself.
Even though it might be a rather universally held assumption that I only experience this particular person that I do now, i.e. E, it is not inconceivable, and therefore it is possible, that I experience multiple different persons.
Just because I experience a memory of a certain experience, it does not follow that experience was actually mine. For one, I might misremember that this was an actual experience which belongs to the perspective of the person that I am (for example, if I have a false memory), but more salient to our discussion is the possibility that the experience is part of that person-perspective, but it was live to some other subject, or not live at all. Neither does it follow that just because I do not experience a memory of having a certain experience, that I did not experience that experience that I do not currently remember. For example, it’s likely that I dream every night, but I cannot remember my dreams most of the time. As a child, E went to kindergarten for the first time, and that experience was likely present like this current moment is present, but I have no memory of it. It is also very likely that I experienced many things that I do not even know about anymore: I know that I must have gone to kindergarten for the first time, and that I did dream last night, even though I don’t remember how it went, but there are probably many things that I experienced that I don’t even remember not remembering.
In the same way, I might have been some other person, even though I currently cannot remember it. Because person-perspectives are (normally) cut off from each other by the continuity of content, by memories, while experiencing some momentary perspective that is a part of some person-perspective, I have no memory of experiencing another person-perspective, simply because those memories are not part of the perspective which I currently experience. And even though I can be sure about the contents of my present experiences, which are of this particular person, and even though I have memories that belong to this particular person and seem to be about her experiences at other points in time, this does not mean that it was actually me (or anybody) who experienced these experiences – from the evidence that is available to me, it is just as possible that it was some other subject that experienced them, and this subject that is me only started existing this morning (i.e. I only experienced E’s perspective starting this morning), or even that the memory does not refer to a real past experience at all, i.e. it only corresponds to some phenomenal qualities which are an unactualized part of E-perspective.
If one accepts the analysis of phenomena described above, because the subject is necessary for any experience to take place, the existence of any experience testifies to a subject’s actual existence and constitutes its proof. That one’s own conscious experiences (phenomena) exist is self-evident, albeit only to that particular subject. So there exists at least one subject, that which experiences this, i.e. the subject that is me – it is certain that E is not a zombie at this moment. It is usually assumed that beyond this current experience, there were and will be other experiences which will be live to me as this one is, but also that there are other experiences which will never be live to me, which would entail there being some other (at least one) subject. But this assumption might be wrong, and I might be the only subject that will ever exist, i.e. it might be the case that all experiences are my experiences, in other words that all actualized perspectives are actualized only in me.
In this paper, I use the name subject solipsism to refer to this thesis. Note that subject solipsism does not entail that all other people are zombies or that they do not exist, only that if they are not zombies, they are me, i.e. they are experienced by the subject that I am. This means that if you are not a zombie (which is obvious to you), then you are me: that is, the subject that is me is identical to the subject that is you. If subject solipsism is not true, then some form of subject pluralism must be true.
It seems to be our common sense intuition that there are multiple subjects, and that every subject experiences only a single person-perspective, and no two subjects experience the same perspective. But even though it is possible there is only one subject per person, it’s also possible that the same person (even our own person) is experienced by multiple subjects simultaneously so to speak, meaning there might exist multiple copies of otherwise qualitatively identical (but numerically distinct, of course) experiences, i.e. a particular perspective might be actualized multiple times in different subjects, that is have multiple actualizations. It might also be the case that a subject experiences multiple person-perspectives. For example, I might actually have been (or, will be in the future) some other person before I was E, just as I could have been (and probably was) a 7-year old E, even though I cannot remember anything from that age (or, at least I currently don’t remember having any memory that is of an event tagged as having occurred when I was 7 years old).
We can come up with even more exotic possibilities about how multiple subjects can be distributed among person-perspectives, or person-perspectives among subjects: perhaps some persons do not have any subject at all that experiences them, i.e. they are zombies; or their person-perspectives are only partially actualized; or they have multiple subjects in succession; or any combination of these possibilities.
To illustrate this, for example, it is possible that there are altogether only 7 subjects; 5 of which experience all persons except for one person, in 5 different streams (i.e. each person-perspective but one is actualized 5 times, in 5 subjects), with the experience of the remaining person split between the 2 remaining subjects so that one subject experiences the person from age 0-3, then the person is a zombie for several years, and the rest of their life is experienced by the remaining subject. This would mean that the sum of all experiences would consist of 5 qualitatively identical sets –one for each of the five subjects– corresponding to the experience of all existing persons except for one, and a set of experiences of the remaining person split between two subjects. For example, if there were altogether 100 person-perspectives, 99 of them would be wholly and multiply actualized –between them, there would be 99*5=495 full actualizations–, and one person-perspective only partially actualized, and 3 distinct subject-perspectives yielding 7 actualizations (one for each subject).
There is an infinite number of scenarios like this – and although amusing and possible, because of their arbitrariness, all of them are (arguably) rather unattractive as hypotheses about the distribution of subjects and persons go, unless one considers whimsicality to be a good criterion for judging between hypotheses.
4. Brains and subjects
Experiences are generally considered to be the products of brains, i.e. certain sufficiently complex interconnected temporally extended physical structures. A brain corresponds to some brain-perspective, even though theoretically a brain can be a zombie and not correspond to any experience, in which case the brain-perspective would not be actualized. It could also be actualized in multiple subjects: either in multiple actualizations (so that there would be multiple “streams” of experience with identical content), or in parts (e.g. first half of the perspective could be experienced by one subject, the second by some other subject).
Because brains correspond, at least under normal circumstances, rather well to persons, each brain-perspective is then also a person-perspective, and because it is expected to be actualized, and expected to be actualized in a single subject, it is also asumed to be identical to some subject-perspective. So it is expected that each brain generates (i.e. causes; or at least corresponds to) a set of experiences which are an actualization of some person-perspective, and an actualization of some subject-perspective: so a particular actualization of some brain-perspective, a particular actualization of some person-perspective, and a particular actualization of some subject-perspective have the same referent (some set of experiences which 1) have the same subject, 2) are of the same person, 3) correspond to all the conscious brain states of a single brain).
In other words, because the brain is assumed to cause experiences, not just to correspond to some unactualized perspective, it is assumed to also generate (or at least correspond to) some (one only) subject, in which the brain-perspective is actualized. On this view, all the experiences generated by some brain constitute an actualization of some particular, and only one, subject-perspective.
A single person-perspective then corresponds perfectly to some subject-perspective, i.e. its actualization is experienced by the same subject (and only one subject) throughout, so that upon death of that person the subject ceases to exist together with the person it experienced, and there isn’t anything that that subject experiences that does not belong to that person-perspective. If this view is true, then there would be as many subjects as there are brains (and other analogical, experience-producing, or with experience perfectly correlated, physical structures, for example machines with this ability).
(1) “Brains ground subjects” thesis: 
- (One subject, one brain:) Every subject experiences only a single brain.
- (One brain, one subject:) Every brain is experienced only by a single subject.
This means that every subject-perspective consists only of the momentary perspectives identical to those of some single brain-perspective. More strongly, every subject-perspective is contentually identical to some brain-perspective, which prevents there being momentary perspectives in some brain-perspective which are not actualized in that subject. There is only one subject in which any particular brain-perspective is actualized: all brain-perspectives only have one actualization each, and each in a different single subject.
If (1) holds, then some experience is mine only if it is an experience of the same brain/person that I am experiencing now (i.e. E), and there is no other subject that experiences this brain/person. Because this that is happening now, i.e. my momentary experience, is a partial actualization of the E-perspective, it follows that my subject-perspective is (contentually) identical to E-perspective, and my subject-perspective and E-perspective are both actualized only once (unless there exists somewhere a copy of E), and these actualizations are identical, i.e. they are the sum of my experiences. So the momentary perspectives which make up E-perspective and my subject-perspective are the same, and this particular sum of momentary perspectives is actualized only once, in me.
On this hypothesis, a subject is assumed to be bound to some particular brain and only lasts as long as that brain does. If (1) is true, then a subject comes into existence when a brain generates it for the first time, exists as long as there is any structure continuous with that brain that is capable of generating experiences, and ceases to exist when there is no longer any structure continuous with this brain capable of generating experiences, i.e. presumably at physical death.
For example, on this view, the subject that I am, S1, now experiences the perspective corresponding to an entity physically and psychologically continuous with (and thus, identical to) E’s brain from the first time she gained consciousness, wakes up as her every day, and will cease to exist upon her death; there is another subject, S2, which experiences some other person, say, the reader of this text that is not E, and S2 will cease existing when this person ceases to exist, i.e. when the brain that corresponds to this person stops producing conscious experiences (or, when there will no longer be any physical structure capable of producing experiences continuous with the structure that originally gave rise to S2); and S1≠S2. So there are as many subjects as there are person-perspectives, which is as many as there are persons (assuming some of the people in question don’t happen to be copies of each other and live the same lives), and there are as many persons as there are brains (or any consciousness-producing physical structures).
The problem with this view is that whereas interconnected physical structures are divisible and fusible, subjects are not.
Consider the fission, fusion, and copy scenarios:
(Fission: ) People, especially children, who undergo hemispherectomy usually do not have their cognitive functions impaired, and their personality and memories are not affected; they are easily considered the “same” person after the surgery. Is the subject who experienced the person before the surgery also experiencing that person after the surgery? If experiences are generated by brains and the subject generated by that brain persists as long as the structure remains functioning, then it would seem that it is. But what would happen if instead of destroying the removed half of the brain it was put in control of some brainless body?
Each of the two resulting structures generates its own experience, its own perspective, so that it could be said that the perspective of the original brain is now split into two streams – and both structures are (equally) continuous with the original structure. However, the subject cannot divide itself into two subjects: I either experience something, or I do not. But then if the subject experiences both the resulting structures, this means it does not correspond to a single interconnected physical structure, but can supervene on multiple such structures at the same time. So if subjects are entities that supervene on a single interconnected physical structure (i.e. brain), then a subject cannot continue to experience both halves of the brain wherefrom it emerged.
Therefore, it would seem it could continue to experience only one half. But which one? Assuming both halves are equally big and functional, where does the subject stay? To decide for one or the other seems arbitrary. Does the other half remain a zombie, or does it at some point generate a new subject? Either way, because both halves are continuous with the original structure, if the subject experiences only one half, then (1) is not true.
Alternatively, it can for some reason cease existing upon fission, and each of the halves of the original structure can give rise to a new subject, or remain a zombie-brain – but each of the halves is continuous with the original brain, so they both should preserve the same subject, therefore in this case also (1) would not be true.
So every one of these options contradicts (1): if I experience both the resulting structures, then I cannot be the product of a single interconnected structure (a brain); if I experience one or neither of the resulting structures, then I cannot be the product of a single continuous structure, because both halves are continuous with the original brain. So it would seem (1) cannot be true.
Perhaps a single brain gives rise to two (or even multiple) subjects, and on fission the subjects are distributed into the resulting structures. But what would determine which subject gets to experience which resulting half of the brain? The resulting half-brain would only hold one subject, which, again, contradicts our new starting presupposition that a brain gives rise to two (or, multiple) subjects. (Perhaps it would spontaneously create as many new subjects as it was missing?)
(Fusion: ) We can also imagine splitting brains of two persons in half and joining one half of the first brain to one half of the second brain, destroying the two remaining halves: how many subjects would be experiencing the resulting structure? Will the resulting fused brain hold two subjects, experiencing the same perspective in parallel? But this would mean that a brain (a single interconnected structure, in this case consisting of two halves originating from two different brains) can give rise to (or correspond to) multiple subjects, which, again, contradicts (1). If not, then the continuity criterion is not upheld. So it seems, again, (1) cannot be true.
(Copy: ) If E’s brain is destroyed and after some time put back together, would I experience the resulting perspective? Obviously on (1), I would not, because the brains are not continuous with each other. If I do, then the continuing survival of a subject is not bound to a continuity of a particular structure (brain), but perhaps that very same subject arises whenever there is a structure which is structurally, or perhaps also materially, identical to a structure that was continuous with whatever structure first gave rise to the subject that I am. But then imagine we take a brain and let it be continuous with every conceivable brain-state (i.e. we let it experience “everything”), and let it “recycle” all the material in the universe for every conceivable brain-state. Then any brain-state we recreate in some substrate should hold the same subject as the original brain, because it is made of the same matter, and is the same structure as some brain-state of the original brain. Indeed, any new person that is born would have the same subject as this original brain, because they could only have brain-states which would be structural and material replicas of the original brain-states of the original brain.
Perhaps only the pattern is what is relevant, regardless of what matter it is made out of – in which case it would seem it could be possible for the same subject to experience multiple structures at once, because the same pattern could be created simultaneously in multiple material substrata (which contradicts (1)).
Even if matter, too, is relevant, then theoretically, because the matter out of which my brain is made out of is continuously being replaced during my lifetime, we could, while I’m still alive, recreate a structure of some younger E’s brain, say, when she was 4 years old, of which the matter has already been replaced: again, we would have two structures (the original E brain and the copy of her brain when she was 4 years old) which should generate (be experienced by) the same subject.
If the continuity criterion for the identity of brains holds, if a continuous structure is associated with/generates/is experienced by the same subject throughout its existence, then a subject can experience multiple structures at once (as illustrated by the fission example), so it does not necessarily correspond to a single interconnected structure; and it can “share” a brain with another subject (as illustrated by the fusion example), so the one brain-one subject criterion cannot hold.
On subject solipsism, continuity is preserved, and also, unilaterally, the one-to-one correspondence: if there is only a single subject experiencing everything there is to experience, then every brain is experienced only by a single subject, and all continuous structures are experienced by the same subject (the only one that exists) throughout. This does not preserve the other side of the one-to-one correspondence, because a single subject would then experience all the brains.
5. Subjects and physical objects
As articulated in more detail in the previous section, it would seem most people, at least in the Western world, expect that they will experience only those experiences which are bound to the brain that is associated with, or gives rise to their experiences now, i.e. are part of the brain-perspective that is currently theirs. They expect no experience to be live to them (to the subjects that they are) unless it is an experience generated by the brain of the person they currently are, the person their experience is currently centered around. If this view is true, it would imply (or at least is consistent with the hypothesis) that their subjectivity is somehow bound to a particular brain: a particular pattern in particular matter, or perhaps just a particular pattern. The matter and the pattern of course change from moment to moment, yet the structure remains continuous (i.e. the temporal parts of the temporally extended object we label “brain” are continuous with each other), and therefore is considered “the same” structure, even if all its material parts were gradually replaced, and the pattern radically restructured. Two physical objects (including brains), as material aggregates, at two points in time, are not identical in virtue of having literally the same properties, i.e. being literally identical in everything that constitutes them: their identity is imposed on them by their being simply, by fiat, by some experiencer, recognized as the same object, made up of many different temporal and spatial parts, based on sufficient similarity and/or continuity, which facilitates (or even makes possible) interaction with them.
It would seem that objects have no objective existence outside of experience: their irreducible material constituents might, but for an object in the common sense of the word to exist, it has to be cut out, conceptualized as an object; boundaries have to be drawn into the world. An object is therefore not just an aggregate of separate parts, but an aggregate upon which a unity was imposed by some mind, i.e. an aggregate conceived as a unity, an aggregate united. Objects are made out of “atoms” (in the sense of a fundamental, indivisible entity), but they are not reducible to some multitude of atoms in the sense that they are identical to some multitude of atoms. The act of cutting out, of drawing boundaries, is what makes a multitude an object. Boundaries of objects are arbitrary and drawn based on convenience. That’s why we arrive at ambiguities when we consider liminal scenarios: heaps of sand and Theseus’ ships, but also fused and divided and copied persons and brains – scenarios which make it evident that the applicability of our concepts, –even though they (our concepts) are under normal circumstances, for practical purposes, usually perfectly sufficient to make sense of the world by cutting it into discrete parts, upon which we can act and about which we can communicate– has its limits. Here our distinctions, useful and easily made under normal circumstances, are rendered inappropriate, our criteria yield counterintuitive results or are inapplicable, and thereby it is made evident that we are not dealing with “real” objects that exist “out there” in the world without our putting them there, so to speak.
And herein lies the problem: there is no inherent identity in objects whose identity derives from continuity, but there is an inherent identity in the subject.
If E is truly experienced by the very same subject that she was experienced by when she was 7, because there was nothing identical to something physical now existing that could give rise to the subject that I am –not identical in the same way that the subject that I am is identical to the subject that I am at some other time– it’s hard to see how some (for example, my own) subjectivity, the thisness of some experience, could arise from something physical, given that (e.g. my) subjectivity is precisely the same now as it was then. Yes, there is the same person, E, and the same brain, E’s brain, but this is not an identity inherent in matter, but an identity of a certain temporally extended object derived from continuity of ever-changing material parts, an identity imposed (by some experiencer) on the matter/pattern.
But the subject does not have this kind of “imposed”, or derived identity. If subject A is identical to subject B, it is not in virtue of it consisting of the same parts, or in virtue of being continuous with some other subject at some other time, but because it simply is the same subject, the same thisness: subjects have no parts or internal properties, because the subject is empty, in itself featureless – so there is nothing that could even be continuous between a subject at T1 and T2 that could make it the same subject. Indeed, subjects exist “at different points in time” only in virtue of the content of the experience that is actualized in them – time (it would seem) does not exist at the level of the subject, but is experienced, or derived from experience. The subject just is the particular liveness of now, the thisness, the presentness – not the content of thisness, i.e. that which is “this”, “now”, but the thisness itself.
That does not mean there are no other thisnesses – if there are other subjects, there must be. But this is not a property of subjectivity, that is what subjectivity is. If there are multiple subjects, they are not different subjects in virtue of having different (non-relational) properties.
So some subject A is not the same subject as some subject B because they are continuous: if they are the same, it is simply because they are identical, they are the same subject, even though what it experiences changes, in a similar sense that the universe is identical to itself, regardless of how much it changes internally, or a physical fundamental particle (if there are such things) are identical to themselves, regardless of what relations they enter into. It would seem subjects are irreducible and indivisible, and therefore fundamental entities.
Any phenomena-producing structure must have an inherent unity: because a phenomenon either does or does not belong to a particular subject. Because my subjectivity doesn’t come in degrees, but either is or is not, if it is an emergent property of matter, there must be some corresponding binary state inherent in matter (not one imposed on it by an experiencer) so that it either gives rise to my subjectivity or it does not.
A subject cannot exist more or less, it has no parts, and it does not have arbitrary boundaries: it is an atom. But there are no ordinary physical objects which are atoms in this sense, because ordinary physical objects have imposed boundaries. The physical fundamental particles (if there are any such things) are too small to be that which corresponds to the subjective experience (and therefore also subjects) of some (macro-)personal perspective: this gives rise to the famous combination problem of micropsychism (see e.g. Chalmers, 2017). The other real “atom”, in the sense of a binary existent which admits of no degrees, but must either exist, or not, is the universe as a whole, even though the universe, as opposed to subjects and atoms, has parts and undergoes internal change.
So if subjectivity corresponds to anything physical (i.e. if consciousness is an irreducible property of matter), then it would seem we are left with cosmopsychism (see e.g. Shani 2015, Albahari (forthcoming)), which admittedly arrives with its own set of problems. It would seem that cosmopsychism yields subject solipsism: brains do not generate subjects, but only create experiences by providing phenomenal qualities which are then actualized in the “cosmic subject”. Indeed brain states seem to correspond well with the contentual aspect of experience, unlike with the subject: if brains actualize consciousness, then brain states can correspond to momentary perspectives (i.e. constellations of phenomenal qualities).
Alternatively, subjectivity does not need to correspond to anything physical, in which case we are left with idealism (and perhaps also some versions of dualism?): this seems to leave our options open for either subject solipsism or subject pluralism.
To inquire about the continued existence of a subject is to inquire about a fact about how the world is. There is a single criterion by which the continued existence of a certain subject can be judged: is there any experience that is live to this subject? Is there any experience that is mine? If yes, then I exist; if no, then I don’t.
Because we don’t know how subjects work, how they are generated, and when they cease to exist, we cannot know the answer to questions about their survival (and vice versa): what is worse, because of the inherently private nature of subjectivity, we probably won’t ever be capable of answering these questions with other than speculative answers.
I can never know not only whether a person I interact with has the same subject they had yesterday, or whether they even have a subject –they might very well be a zombie–, or how many subjects they have: I cannot know even about myself that I existed yesterday, or that I was experiencing this particular person that I am experiencing now, and I cannot know how many subjects experience the perspective that I am experiencing now.
What I can know, however, and I can know this with absolute certainty, is that I exist, now, and as this particular person, experiencing this particular momentary perspective, that is, this, even though I cannot know whether the person-perspective that this particular this is a part of will be actualized in my subject in its entirety. So, at any point in time, I can only know about my continuing existence (as long as I continue to exist), but I cannot know whether I existed at some other point in time, or will in the future, even if the person (brain) that I currently am would continue to exist. The survival of this person that I am does not entail my survival; my survival does not entail the survival of this person.
There are facts about how the world is that are subjective and private, and inherently unknowable to another subject, or even in principle unknowable, to anybody: for example, “is this person a zombie?”, or “are there any things that are inherently undetectable and unknowable by humans?”, but also “did I exist a year ago?”, “will I survive the death of this person that I am now?”, and “am I the only existing experiencer?”.
There must be a fact of the matter about these things, but I, at least as I am now, cannot know what it is, and neither can anybody else, if they are like me, or so it seems.
- Albahari, M. (forthcoming). Beyond cosmopsychism and the great I am: How the world might be grounded in universal ‘advaitic’ consciousness. In William Seager (ed.), The Routledge Handbook of Panpsychism. Routledge.
- Chalmers, David (forthcoming). Idealism and the Mind-Body Problem. In William Seager (ed.), The Routledge Handbook of Panpsychism. Routledge.
- Chalmers, David (2017). The Combination Problem for Panpsychism. In Godehard Brüntrup & Ludwig Jaskolla (eds.), Panpsychism. Oxford University Press.
- Hellie, Benj (2013): Against Egalitarianism. Analysis 73 (2):304-320.
- Kolak, Daniel (2004). I Am You: A Philosophical Explanation of the Possibility That We Are All the Same Person. Springer
- Kirk, Robert, “Zombies”, The Stanford Encyclopedia of Philosophy (Winter 2017 Edition), Edward N. Zalta (ed.), URL = <https://plato.stanford.edu/archives/win2017/entries/zombies/>.
- Parfit, Derek (1971). Personal identity. Philosophical Review 80 (January):3-27.
- Strawson, Galen (2011). The minimal subject. In Shaun Gallagher (ed.), The Oxford Handbook of the Self. Oxford University Press.
- Shani, Itay (2015). Cosmopsychism: A Holistic Approach to the Metaphysics of Experience. Philosophical Papers 44 (3):389-437.
- Wiggins, David (1967). Identity and Spatio-Temporal Continuity. Blackwell.
 In this paper, I use the acronym „E“ to refer to this person.
 In this paper, I use „I“, „me“ to refer to the subject of experience that is me, not to Edralis (and „mine“, „my“ to that which pertains to it).
 One might argue that there are no such things as subjects of experience. But if there are no individuating subjects, then all experiences are present in the same way that that this one is present, i.e. it would seem this would amount to subject solipsism. I describe this position below, in the 3rd section of this paper.
 Hellie (2012) chooses a rather fitting epithet to capture this meaning, referring to the immediate and transparent givenness of this that is now, which is shared by all my experiences, when they are present: “‘live’”. What I experience now is live to me.
 The analysis that I work with here is not unprecedented. For example, Strawson (2011) offers practically the same conceptual distinction, distinguishing between the content and the subject of an experience.
 ‘To actualize’ is used in two senses here: in the former case, it refers to the relation between the subject and phenomena, whereas of course subject is already subsumed under phenomena, it is already included in the phenomena, it is what phenomena are made of – like the relation of a rubber ball to its color; whereas in the latter case, because phenomenal qualities and subjects relate to each other as co-constitutors of phenomena, the relation is perhaps more akin to the relation between the color and the shape of a rubber ball (which, together, constitute the (visual aspect) of the rubber ball). That’s perhaps not a perfect analogy, but my point is to bring attention to the ambiguity, the polysemy, of the words like ‘actualization’, even in specific contexts like this, because their flexibility in usage might, of course, easily lead to confusions.
 A zombie is a creature physically and behaviorally identical to a person, but there is ‘nothing it is like’ to be it, i.e. they do not have conscious experience. For an overview of zombies, see e.g. Kirk, 2015.
The person-perspective that corresponds to any zombie is not actualized for that creature. However, it might theoretically be actualized in some other creature somewhere else – for example, if there is an exact copy of that creature somewhere, living exactly the same life, and this creature is not a zombie. The perspectives of these two creatures, because these creatures are copies of each other, living contentually (not numerically, of course) the exact same life, are identical – they are the same perspective. But whereas this perspective is actualized for one creature, for the other, it is not. There is only one actualization of this perspective, which is identical between these creatures.
Assuming brains are what creates consciousness, the actualization of the perspective in question would be created by the copy-of-the-zombie-creature’s brain (which is not a zombie), not by the original zombie-creature’s brain. So there is a difference in causality: if an experience is not actualized for a creature, but say for a different one, even though their perspectives might be identical, what this means is that it (the actualization, the set of experiences) is not generated by the brain of this creature, with “generation” being some kind of causal relation.
 For example, it is perfectly conceivable that after E dies, I will experience E once more, and experience her life once again, which would arguably amount to her being reborn.
 Theoretically, it might have been actualized in its entirety before: for example, if the universe is cyclical and this is not its first iteration, or if there is an exact copy of E somewhere for whom that perspective is actualized.
 Note that if parts of a perspective were actualized in the reverse order, or out-of-order, this would not translate into the experience itself. An experience already includes in itself information about the order of its occurrence if it includes memories. But theoretically, the actual order of those experiences might be different. For example, my next experience might be that of yesterday, and I wouldn’t know any better, because, experiencing yesterday, I wouldn’t remember today, even though I already would have experienced it.
 Note that only a single momentary perspective can be present to a subject at any given moment; so a subject-perspective in its entirety cannot be experienced at once, i.e. cannot be present as a whole, but only in parts, in time. That is, excluding the subject-perspectives which only „last“ a single momentary perspective, if there are any such subject-perspectives.
 For example, take subject A: during its existence, it will actualize momentary perspectives x, y, z, each of them being some constellation of some phenomenal qualities. The (temporally ordered? but this makes no difference to the experience) set of momentary perspectives [x, y, z] now constitutes a subject-A-perspective in virtue of being all the constellations of phenomenal qualities actualized in subject A. This perspective can then become actualized in subject B. The experiences themselves of course cannot be experienced by (actualized in) another subject.
 Note that this certainty, and the reflection on that certainty, and the reflection on that reflection, are also part of that perspective.
 Actually, it might be the case now that there are other subjects beside myself experiencing her perspective.
 which would make those beings conscious, i.e. non-zombies.
 Similarly to how I probably experienced E when she was 13 years old, and when she was 20 years old etc. – I was probably all these Es, even though I am an older E now. In that same way, I might have been some other person, even though I am E now.
 In other words, at the time where this experience was supposed to have happened, E was a zombie.
 Kolak (2004) uses the term “open individual view of personal identity” or “open individualism” to refer to what seems to be an equivalent view.
 Literally, the same subject. It means any pain or joy that belongs to E and that is experienced by me is the pain that is experienced by you, because you and I are identical, the very same entity. When E pinches her skin this is live to you in the same way as when the person that you currently are, reading this, pinches their skin.
 Which means that there is only a single actualization of every person-perspective. That is, unless there are any copy-creatures, living contentually the exact same lives.
 Obviously, we cannot know whether this is or isn’t the case by looking at some person. The person as we know them is, or rather is abstracted from, a set of our experiences (visual, tactile, auditory, and some more subtle), which we assume correspond to some person-perspective. We expect this person-perspective to be actually experienced by that person, i.e. that there is also a corresponding set of experiences that are actualizations of that person-perspective, which are generated by a (real, objective, external) brain that corresponds to this person, or rather their brain, in our experience. But it (the person-perspective) might as well not be actualized, or there might as well be several or many actualizations of it.
 This view seems to correspond well with the view of personal identity called closed individualism by Kolak. See Kolak 2004, pp.7
 This is a hypothesis about which experiences are mine, given the experience that I have now; it is not an answer to the question of why I am this particular person, which Hellie (2013) calls the “vertiginous question”: „The Hellie-subject: why is it me? Why is it the one whose pains are ‘live’, whose volitions are mine, about whom self-interested concern makes sense? That thing there in the objective world: what is so special about it? Why doesn’t some other subject of experience there in the objective world ‘go live’ in this way […]?” In other words, what makes it the case that I am experiencing the world from this particular perspective? If it is true that I correspond to some particular physical structure, that I am generated from/by some particular lump of matter: this seems entirely baffling and arbitrary! Whatever might it be about this particular brain, this particular structure that gave rise to me, when all other structures and lumps of matter that ever were or will be did not? Why are the experiences of this particular person mine, unlike those of other people? (If we created a copy of my brain, would that copy also be experienced by me? How about if we created a copy of my brain as I am now, after it is destroyed, from the same matter that it is made out of now?) Note that on subject solipsism, the question is dissolved: I experience all the brains, all the people, all perspectives, so it’s no surprise that I also experience this one. Of course, then another question poses itself: why this person, this moment now?
 Does the structure constantly recreate numerically the same subject, or is the subject created only once and then somehow sustained in existence? Perhaps, instead of creating it, the brain somehow only “reaches out” to the subject, which is really “somewhere else” – but in what sense could a subject exist when there is no experience that it actualizes, when there is nothing that could play the role of the this?
 These scenarios were introduced and are treated primarily in the context of examining personal identity, e.g. in Wiggins, 1967 and Parfit, 1971.
For a very impractical conception of personhood, we can take subject as the criterion of personal identity: Person x at t1 is identical to person y at t2 iff the momentary perspective that corresponds to the person x at t1 is actualized in the same subject as the momentary perspective corresponding to the person y at t2. In other words, if x is experienced by S1, and y by S2, x=y iff S1=S2. If a perspective corresponding to some person at some time is actualized in multiple subjects at once, whether this person is or is not identical (on this view) to some other person depends on which subject we have in mind as the criterion of personal identity. Note that it is impossible to determine both from outside (from another person’s or subject’s POV), and from inside (from the person x or y’s POV, i.e. from the POV of the subject that experiences x or y, if there is such a subject) whether this identity holds or not, which arguably does not make it a very good, or at least practical, criterion of personal identity.
S1 and S2 are not identified as identical in virtue of continuity of some features, but because they just are the same thing: they are a certain way things (phenomena) are present. S1 and S2 are identical simply if they are the same subject. Indeed apart from the fact that if there are multiple subjects, only one of those subjects is me (and only one of them is you etc.), subjects are in themselves devoid of any intrinsic distinguishing features. (Of course if there are multiple subjects, they also might differ in respect of which phenomenal qualities they actualize (i.e. which phenomena they constitute), and so they differ in relational properties.) Note that on this view of personal identity, a person-perspective is by definition identical to some subject-perspective.
But impractical as though this conception of personal identity might be, it seems to me when people ask about their own survival, it is oftentimes actually the survival of the subject which they really have in mind: “If my brain is bisected and put into two different bodies, upon awakening from the surgery, from which pair of eyes will I see?” “If I was teletransported, will the experiences of that person on the other side be live like this experience is now, or will it just be a copy/clone of me?” From the perspective of a third person, this does not make any difference. But for me, for the subject of the person undergoing these scenarios, it makes all the difference: it is a question of life and death, of continuing existence or demise.
At least some people seem to have no problem understanding the concept of tabula rasa reincarnation, and so they seem to be able to operate with this criterion in mind, and consider it not only coherent, but existentially meaningful.
 I.e. have one hemisphere of their brain removed, usually in order to control seizures in severe cases of disorders such as Rasmussen’s encephalitis.
 The act of unification by some mind of parts or atoms into a single object is necessarily a part of what an object is. A bunch of atoms might be materially identical to an object, but it is not, in itself, an object.
 Note that “physical” here refers to a certain kind of phenomenal, which is expected to more or less truthfully represent the non-phenomenal, i.e. the external (that which existst independently of any mind/subject/conceptual scheme). Of course subjectivity cannot in itself arise from phenomena, because it constitutes phenomena: rather, the expectation here is that the phenomena (phenomenal brains) correspond to non-phenomena (non-phenomenal “brains”) which generate consciousness. Because the physical objects in our experience change constantly, and given they are truthful representations of the non-phenomena, the non-phenomena are therefore also assumed to be in constant flux, even though it’s hard to see how something which is not conceptualized as consisting of interacting parts (for which concepts seem to be necessary) can even be meaningfully said to be in flux, i.e. changing. (But perhaps it’s not incoherent to apply concepts on the non-phenomenal to make sense of it, while understanding the distinctions that we make aren’t “really” there? And if we assume that phenomena are representations of non-phenomena, we already by necessity conceptualize the non-phenomena by bringing them into (causal, representational) relations with phenomena.)
Also note there is a difference between 1) the non-phenomenal, external, “objective” brain (let’s call it brain B), which is expected to actually give rise to consciousness, and the corresponding non-phenomenal body and person (body B, person B), 2) a representation of brain B/body B/person B (as phenomena) in some other person’s POV (i.e. in some (actualized) person-perspective of some other person, i.e. not that of person B, whose body make up the center of their perspective), 3) representations of body B and person B (as phenomena) in the person-perspective of the person B (which is usually centered on the body of person B), 4) the phenomena arising from (non-phenomenal) brain B (i.e. actualized person-perspective of person B – these usually include 3) above). The distinction needs to be made between some non-phenomenal object (e.g. brain, body) and its phenomenal representations in different persons (perhaps even different subjects). That which I call E is not that which you call E, and is not that which is E out there in the world.
Also, obviously, my phenomena (e.g. a brain that I perceive) cannot be the cause of your phenomena. Rather, we expect that which I perceive (=some phenomenon. i.e. your brain as it appears in my consciousness) to be the representation of that which creates your consciousness (i.e. your brain as it is outside of anybody’s consciousness). Of course, “perceive” is an ambiguous verb, as we can also use it to refer to the relation I have to something external (in the sense of non-phenomenal) which is represented as a phenomenon: I A-perceive some phenomena, but do not A-perceive non-phenomena which give rise to them; but I B-perceive the non-phenomena of which representations I A-perceive, but do not B-perceive the phenomena, i.e. the representations. Two persons (or subjects) can B-perceive the same thing, but cannot A-perceive the same thing, because the things which are A-perceived are phenomena (or, rather, phenomenal abstractions, because, again, we do not have a phenomenal experience of an object in its entirety, but only in a certain moment, from a certain angle, in certain light etc., i.e. only its temporal slices are actually phenomena) and therefore private.
 With the exception of relational properties.
 The matter is complicated further on subject pluralism.
 By macro-personal here I mean a personal perspective in the usual sense of the word, that of a perspective of e.g. a human or an animal, i.e. an object made out of many atoms. Chalmers (forthcoming) makes a distinction between macro- and micro-subjects: on my analysis, there is no distinction of “size” in the subjects themselves, but they could be considered micro- and macro- in virtue of the kind of subject-perspective (i.e. what phenomenal qualities) they actualize; if (physical) atoms are conscious and only have some sort of primitive experience (e.g. consisting of only a few phenomenal qualities), then they can be considered micro-subjects in this sense.