There are three versions of the subsumptive unity thesis: the pairwise version, the general version, and the total version. There are correspondingly three versions of the logical unity thesis, holding either that there is logical unity among either any two states of a subject at a time, any set of states, or the complete set of states. Or more directly: Pairwise Logical Unity Thesis: Necessarily, for any two phenomenal states had by a subject at a time, the subject has a phenomenal state that entails both original states. General Logical Unity Thesis: Necessarily, for any set of phenomenal states of a subject at a time, the subject has a phenomenal state that entails each state in the set. Total Logical Unity Thesis: Necessarily, for any conscious subject at a time, the subject has a phenomenal state T such that for any phenomenal state A of the subject at that time, T entails A. As before, it is clear that the general thesis entails the pairwise thesis and the total thesis as special cases. The total thesis also entails the general thesis and the pairwise thesis, since a state that entails all phenomenal states of a subject will also entail any pair or any set of states. Arguably the pairwise thesis does not entail the other two theses, because of the formal possibility that there might be entailing states for any finite set of states, but not for infinite subsets. We can start by focusing on the total logical unity thesis, since this corresponds most closely to the total phenomenal unity thesis, which arguably captures the central intuition behind the unity of consciousness. Intuitively, we can think of T, the entailing state in the thesis, as the subject's total phenomenal state, capturing what it is like to be the subject at that time. If such a state exists, it will fulfill the requirement of the total logical unity thesis. One can also approach the matter in logical terms. Let us say that the conjunction of a set of states is a state C such that necessary, a subject is in C if and only the subject is in each of the states in that set. (Like entailment, conjunction is fundamentally a relation among state-types, and derivatively a relation among state-tokens. Note also that the conjunction of states is quite different from conjunction of the contents of states.) This identifies C at least up to mutual entailment. For present purposes, it is useful to assume that when two states A and B mutually entail each other (i.e. when necessarily, a subject is in A if and only if the subject is in B), then the two states are identical. If so, then C is identified uniquely. Nothing that follows rests essentially on this assumption; one could rephrase things in terms of equivalence classes of states.

;  Let us say that a set of states is conjunctively unified when the conjunction of the members of that set is itself a phenomenal state. Then from the discussion above, it follows that the total logical unity thesis is equivalent to the claim that the set of a subject's phenomenal states is conjunctively unified: Total Conjunctive Unity Thesis: If C is the conjunction of all of a subject's phenomenal states at a time, then C is itself a phenomenal state. As before, someone might think that a thesis of this sort is trivially true, but this would be incorrect. It is trivial that for any set of phenomenal states of a subject at a time, there will be a conjunctive state C that entails each of the original states. But it is nontrivial that C will itself be a phenomenal state. That is, it is nontrivial (although very plausible) that there will be something it is like to be in C: some global phenomenal character that a subject will have if and only if the subject is in C. Those who deny the original unity thesis will deny the existence of such a phenomenal character, and so will deny that C is itself a phenomenal state. In effect, we have seen that the original phenomenal unity thesis is equivalent to a thesis about the conjunctive closure of co-instantiated phenomenal states (where co-instantiated states are states had by the same subject at the same time): certain conjunctions of states in this class must also be states in this class. This is very useful, since conjunctive closure is amenable to relatively straightforward analysis. One can also formulate conjunctive closure theses that are closely related to the other versions of the logical unity thesis. There is a pairwise version, and a general version: Pairwise Conjunctive Unity Thesis: For any two phenomenal states of a subject at a time, their conjunction is a phenomenal state. General Conjunctive Unity Thesis: For any set of phenomenal states of a subject at a time, their conjunction is a phenomenal state. These theses are not quite formally equivalent to the corresponding versions of the logical unity thesis. To see this, note that it is at least a formal possibility that two states might be logically unified but not conjunctively unified. For example, it is at least formally possible that the conjunction of all of a subject's phenomenal states might be a phenomenal state, but that the conjunctions of certain pairs and subsets might not be. If so, then these pairs and subsets will be logically unified but not conjunctively unified. In this case the pairwise and general conjunctive unity theses will be false, but the the pairwise and general logical unity theses will be true. However, it is clear that these conjunctive unity theses entail the corresponding versions of the logical unity thesis. And they are interesting and plausible theses in their own right. The first says that for any two phenomenal states A and B of a subject at a time, there will be something distinctive it is like to be in A and B: that is, a distinctive conjoint phenomenal character that a subject will have if and only if the subject is in both A and B. The second says the same thing for arbitrary sets of co-instantiated phenomenal states. These theses are not formally trivial, but they are highly plausible theses about phenomenal consciousness. All three theses are simple and elegant. The pairwise conjunctive unity thesis says that the class of phenomenal states is closed under pairwise co-instantiated conjunction: the conjunction of two co-instantiated phenomenal states is a phenomenal state. The general conjunctive unity thesis says that the class of phenomenal states is closed under general co-instantiated conjunction: the conjunction of any set of co-instantiated phenomenal states is a phenomenal state. And the total conjunctive unity thesis says that the class of phenomenal states is closed under maximal co-instantiated conjunction: the conjunction of a maximal set of co-instantiated phenomenal states is a phenomenal state. The total conjunctive unity thesis remains the core version of the unity thesis, but all of these theses are plausible and useful. Each of them can be used as a tool in assessing the status of the unity of consciousness, in assessing its consequences, and in assessing its compatibility with various theories of consciousness.

It should be noted all of these unity theses are stated simply in terms of the notions of phenomenal state, of co-instantiation, and of conjunction. And the notion of a phenomenal state is tied constitutively to the notion of there being something it is like to be a given subject, or to be in a given state. So we have an account of unity that requires little more than the existing "what it is like" conception of phenomenal states. This stands in tension with a claim in a very interesting analysis by Hurley that the unity of consciousness cannot be characterized "subjectively", and that suppositions about the structure of consciousness are not captured by the "what it is like" test, so that we need to appeal to further "objective" properties to give an account of unity. This claim is grounded in the claim that in a case where unity breaks down, there is no "what-it-is-like" that captures the structure of a subject's consciousness. Hurley backs up this claim by considering two cases: (i) two subjects, one experiencing red and hot, the other experiencing red and dizzy; and (ii) a partially unified single subject, in whom red and hot are unified, red and dizzy are unified, but hot and dizzy are not. Hurley argues that no "what it is like" facts can distinguish these two cases. But from the claim that there is no what-it-is-like that characterizes a disunified subject, it does not follow that one cannot characterize unity in what-it-is-like terms. Indeed, following Hurley's own claim, one can hold that unity breaks down precisely when there is nothing it is like to have all a subject's conscious states simultaneously. We can distinguish case (i) from case (ii) above by noting that in case (ii), both subjects have a phenomenal state that subsumes all their phenomenal states, whereas in case (i), the subject has no such phenomenal state. Of course, our characterization of unity appeals to something more than phenomenal states themselves: it appeals to subsumption, and to co-instantiation in a subject. Perhaps Hurley would count these notions as in some sense "objective". There is no point arguing over terminology here, but we can at least note that subsumption is a phenomenal relation, fixed by phenomenology alone: if A subsumes B, then the phenomenology of A guarantees that it subsumes B. And subjects are simply the bearers of phenomenal states. So we are staying quite close to home in characterizing unity this way.

Hurley might extend her argument by suggesting case (iii): a bifurcated subject with two different (but indistinguishable) tokens of red in separate streams. In this subject, red1 is unified with hot, red2 is unified with dizzy, and no state in either pair is unified with a state in the other pair (Hurley 1998, p. 166, seems to point toward such a case). If (iii) is possible, one could argue that it could not be distinguished from (ii) by talk of subjects and their phenomenal states alone. We would need to appeal to the identity of phenomenal states: a single "red" experience is involved in both complex experiences in (ii), but not in (iii). There are a number of things one could say in response. One might concede that "what it is like" talk cannot distinguish the two different cases of disunity (ii) and (iii), but hold that it can nevertheless distinguish unity from disunity, which is the most important work we need it to do. If the unity thesis is true, then cases of disunity will be impossible, and distinctions among impossible cases will not matter to characterizing the structure of consciousness. More deeply, one can suggest that Hurley's argument shows at best that one cannot distinguish the cases in terms of the distribution of phenomenal state-types. If we appeal to facts about the distibution of phenomenal state-tokens, things are straightforward: there is a token experience that is subsumed by two different complex experiences in (ii), but not in (iii). It may be that (ii) and (iii) will be introspectively indistinguishable, so that the structure of consciousness is not transparent to a subject. But nevertheless, a characterization of the structure of consciousness in terms of phenomenal relations among phenomenal state-tokens is still, in a deep sense, a characterization in subjective terms. Our characterization of unity in phenomenal terms also stands in tension with a claim by Shoemaker (this volume). Shoemaker suggests that if a conscious state is understood as one with a phenomenal property (i.e. one such that there is something it is like to be in it), this leads to "consciousness atomism": the view that the factors that make a state conscious are independent of the factors that make two states unified. Our discussion here suggests that this is false. What it is for two conscious states to be unified can be understood in terms of the existence of a more complex conscious state, where both the simple state and the complex states are states characterized by what it is like to be in them. So the factors that enter into unifying conscious states are the same sort of factors as those that enter into those states being conscious in the first place. At one point, Shoemaker characterizes "consciousness atomism" differently, as the view that "whether a state is conscious will be independent of whether there are other conscious states with which it is co-conscious". The account here is neutral on this claim. For all we have said here, it may be possible for there to be a subject with a single conscious state. This claim does not seem to us to be obviously objectionable, and it is compatible with the more important view that the factors that enter into consciousness are the same as those that enter into co-consciousness. In fact, the definitions of unity that we have given here suggest that any account of what it is to be a phenomenal state will automatically yield a theory of what it is for two such states to be unified. We need simply to apply the theory to the relevant conjunctive states, in order to determine whether they are phenomenal states. In this way, it seems that any substantive theory of phenomenal consciousness can yield unified definitions of consciousness and of co-consciousness. It is precisely because of this that the unity thesis (if it is true) puts strong constraints on a theory of phenomenal consciousness, as we will see.

 Applications of the Unity Thesis

We have already mentioned the objection that the conjunctive versions of the unity thesis are trivial: that is, that it is trivial that the the conjunction of a set of co-instantiated phenomenal states is itself a phenomenal state. It is clear that the thesis is not formally trivial, in that there are many classes of states that are not closed under co-instantiated conjunction: e.g., states of the sort "talking with X", where X is an individual. Closer to home: there are also many classes of mental states that are not closed under co-instantiated conjunction. For example, the class of belief states does not seem to be closed under conjunction. Let us say that a belief state is the state of believing some proposition. Then it is not the case that the conjunction of any set of belief states is a belief state. For example, if A is the state of believing that P, and B is the state of believing that Q, there is plausibly no belief state that a subject will be in precisely when they are in A and B. The only tenable candidate for such a belief state is the state of believing P and Q.

But there are well known reasons to believe that a subject can believe that P and believe that Q without believing the conjunction P∧Q. For example, P and Q might be believed in different "compartments" of a compartmentalized mind. It may even be that for some P, a subject can believe that P and separately believe that ~P, without believing the contradiction P∧~P.

And it seems quite possible that a subject can have many different beliefs without accepting the massive conjunction of the contents of all of those beliefs. If this is right, then the conjunction of co-instantiated belief states will not in general be a belief state. So the class of belief states is not closed under co-instantiated conjunction. It may seem plausible or even obvious that the class of phenomenal states is closed under conjunction. But if so, this is a substantive thesis about the class of phenomenal states, and their difference with other classes of mental states. It may even be a conceptual truth, in some sense, that the class of phenomenal states is closed under co-instantiated conjunction. But if so, this is again a substantive thesis about the concept of a phenomenal state, and a way in which it differs from the concept of a belief state, and of other sorts of states. The substantive nature of the thesis is revealed by the fact that the conjunctive unity theses put a strong constraint on potential theories of consciousness. We have seen that the unity thesis is prima facie plausible, and there there seem to be no strong arguments against it. If this is right, then the unity thesis puts a prima facie constraint on theories of consciousness: they must be compatible with the unity thesis. And in particular, any account of phenomenal states must be compatible with the total conjunctive unity thesis. Whatever phenomenal states are, according to a given account, the class of phenomenal states must be closed under total co-instantiated conjunction. A number of prominent theories of consciousness appear to be incompatible with this constraint. One example is the higher-order thought theory of consciousness, put forward by David Rosenthal (1997) and others. Not all higher-order thought theorists intend the theory as an account of phenomenal consciousness, but we are only concerned with versions of the theory that are aimed at phenomenal consciousness. The central idea of these theories is the following: Higher-Order Thought Thesis: A mental state M is phenomenally conscious if and only if a subject has a higher-order thought about M. Here, a higher-order thought about M should be understood as a thought by the subject with the content "I am in M". The thesis will usually be modified and qualified in some ways. For example, Rosenthal holds that for M to be conscious, the higher-order thought must be brought about in the right sort of way, and in particular must be a noninferential thought. Rosenthal also holds that only sensory states can be phenomenally conscious, so that we would have to insert a rider to that effect in the definition above. This is arguably a mere terminological difference, however, since Rosenthal holds that there will be something it is like to be in a state whenever it is the object of the right sort of higher-order thought, whether the state is sensory or not. In any case, for our purposes we will take the thesis in the simple form above. Our arguments should apply straightforwardly to most modified versions. Is the higher-order thought thesis compatible with the unity thesis? It is easiest to approach this question by considering the conjunctive versions of the unity thesis. The conjunctive versions say that the class of phenomenal states are closed under conjunction. So we can ask: on the higher-order thought theory, is the class of phenomenal states closed under conjunction? We can start by thinking about phenomenally conscious mental states. If A and B are phenomenally conscious mental states, is A&B necessarily a phenomenally conscious mental state? Assuming the higher-order thought thesis, this translates into the following: if a subject has a higher-order thought about A and a higher-order thought about B, does the subject necessarily have a higher-order thought about A&B? That is, if the subject has a thought "I am in A" and a thought "I am in B", does it follow necessarily that the subject has a thought "I am in A and B"? It seems not. It is surely possible for a subject to think "I am in A" and "I am in B", without connecting these into a thought "I am in A and B". We can take a case like those discussed above, in which a subject has contradictory beliefs, knows that she has each belief, but never puts the two together. She might have the thought "I believe P" and the thought "I believe ~P" without ever putting these two together into a thought "I believe both P and ~P". This might be strange or unusual, but there is nothing contradictory about it. There would only be something contradictory here if the beliefs of a subject are necessarily closed under logical consequence; but of course no subject's beliefs are closed under logical consequence. The same is even clearer where total conjunctivity is concerned. On the higher-order thought theory, if a subject has a number of phenomenally conscious mental states, is their conjunction a phenomenally conscous mental state? That is, if a subject is has mental states A_1, ..., A_n, and has the thoughts "I am in A_1",..., "I am in A_n", does the subject necessarily have the thought "I am in A_1&A_2&...A_n"? Again, it seems not. One might reasonably argue that this entailment does not even hold typically, let alone necessarily. That is, it is arguable a typical subject with these higher-order beliefs would not have the complex conjunctive belief. Whatever one says here, it is hard to dispute that it is possible for a subject to have the individual higher-order beliefs without the complex conjunctive belief.

So it appears that if the higher-order thought view is true, the class of phenomenally conscious mental states is not closed under co-instantiated conjunction. This already contradicts the central intuition behind the unity thesis: that necessarily, if there is something it is like to be in each of a set of states, there is something it is like to be in all the states at once. On the higher-order thought view, this thesis will clearly be false. The official version of the unity thesis is stated in terms of phenomenal states, not phenomenally conscious mental states. The analysis of phenomenal states is slightly tricker, since advocates of the higher-order thought view have not usually talked about phenomenal states and phenomenal properties directly. But given that higher-order thought theorists hold that there is something it is like to be in a mental state when the subject has a higher-order thought about it, they presumably hold that what it is like to be in that state is determined by the content of the higher-order thought. If so, it seems that phenomenal properties will be the properties of having higher-order thoughts with certain contents, and phenomenal states will be the states of having such higher-order thoughts. Do phenomenal states, understood this way, satisfy the unity thesis? It seems not, for much the same reason as before. Here it is useful to take the entailment version of the unity thesis: that necessarily, when a subject has a set of phenomenal states, the subject has a phenomenal state that entails each of the individual states. The problem is rather that on this account, there is no reason to believe that phenomenal states, or phenomenally conscious mental states, will always be unified. Certainly it will not be necessary that they be unified, and it seems plausible that in a typical case, they will not be unified. So the higher-order thought thesis is incompatible with the unity thesis. It is clearly incompatible with the conjunctive and logical versions of the unity thesis. It is therefore also incompatible with the subsumptive versions, since any failure of logical unity automatically entails a failure of subsumptive unity. So if the higher-order thought thesis is true, the unity thesis is false. And if the unity thesis is true, the higher-order thought thesis is false. Proponents of the higher-order thought thesis might reply in a number of ways. Most straightforwardly, they might reply by denying the unity thesis. This is a tenable response, since the truth of the unity thesis cannot be taken for granted. But still, there is a strong intuition that the unity thesis is true, so the incompatibility is at least a cost of the higher-order thought thesis. Proponents might also embrace a more limited version of the unity thesis, arguing for example that unity holds typically but not necessarily, or that it holds given contingent facts of human psychology, but not for all possible beings. Here there would still be the cost of denying the intuition of necessary unity, and there would be the added difficulty of defending the claim that unity holds in the relevant range of cases, when there seems to be no obvious reason why complex conjunctive thoughts about all the objects of our higher-order thoughts should typically exist. A higher-order thought theorist might also respond by finding fault with the argument for incompatibility: they might hold, for example, that it is necessary that the class of mental states that are objects of higher-order thoughts is closed under conjunction. This would be a difficult case to make, in face of the apparent possibility of failure of this principle, and in face of the general phenomenon that beliefs are not closed under logical consequence. Finally, a proponent might modify the higher-order thought thesis to make it compatible with the unity thesis. To do so, they must modify the definition of a phenomenally conscious mental states. It could be held, for example, that a mental state is phenomenally conscious when either (i) it is the object of a higher-order thought, or (ii) it is the conjunction of states that are the objects of higher-order thoughts. This sort of disjunctive account would be contrary to both the letter and the spirit of existing higher-order thought views (which hold that a conscious state is one that the subject is conscious of). One could also raise questions about whether this thesis delivers any substantive unity of consciousness, or merely a stipulated sort of unity of consciousness that holds trivially. And so far as the unity of consciousness seems to be a substantive fact about consciousness, one could argue that this modified version of the higher-order thesis does not really account for it. Of course all of this is debatable and could lead to fruitful further discussion. But the prima facie incompatibility between the two theses is at least interesting. It is worth noting that the incompatibility extends straightforwardly to other "higher-order" views of consciousness, including views on which a conscious state is an object of a higher-order perceptual state, or the object of some other sort of higher-order representational state. The existence of a set of higher-order perceptual states does not entail the existence of a complex conjunctive higher-order perceptual state, and the same goes for other sorts of representational states. So if the unity thesis is true, these theses are false, and vice versa. The unity thesis is also incompatible with many representationalist views of consciousness. According to representationalist views, all phenomenally conscious mental states are representational states (that is, states with representational content). This is commonly allied with a further functional criterion to yield: Representationalist Thesis: a mental state is phenomenally conscious if and only if it is a representational state that plays an appropriate functional role. We will focus on this broadly functionalist variety of representionalism. The details of the relevant functional role different between representationalists, but it is typically held to involve some sort of access and control. One can then say that what it is like to be in a mental state is determined by the content of the representional state, on the condition that it plays the relevant functional role. On this sort of view, then, a phenomenal state is a state of having a certain sort of representational state play the appropriate functional role, where distinct phenomenal states are individuated by distinct representational contents. As before, representationalists could respond in a number of ways. They could deny the unity thesis, at cost of denying a strong intuition. They could modify it to apply to a more limited range of cases, at cost of some intuition and perhaps some empirical constraint. (For example, in the Sperling case, this representationalist may have to deny that the subject has a phenomenally unified visual field.) They could modify the representationalist thesis to allow a disjunctive definition on which is stipulated that conjunctions of phenomenal states are phenomenal states, at cost of endangering the substantive status of the unity thesis. Alternatively, they could move to a different sort of representationalism which is not so closely tied to functionalism: for example, it might be held that phenomenally conscious states are representational states whose content is represented phenomenally, or that they are representational states with some other property that is not functionally defined. The resulting version of representationalism might be compatible with the unity thesis (as well as being independently more plausible than the previous versions), at cost of giving up the reductive aspirations of many representationalist views. One might also argue that other nonrepresentationalist forms of functionalism are incompatible with the unity thesis, on the general grounds that there will not be the relevant conjunctive property among states playing the functional role. The details will depend on the details of the functionalist theory, and in particular on the account that is given of phenomenal states and properties. These accounts can vary between functionalist theories, and are often not clearly articulated, so it is difficult to give a general analysis of such theories with respect to the unity thesis. But it is clear that it will be at least highly nontrivial for a functionalist account to satisfy the unity thesis. If what has gone above is correct, then the unity thesis is incompatible with higher-order thought (and other higher-order representation) views of consciousness, with many representationalist views of consciousness, and with many functionalist views of consciousness. So the unity thesis is clearly nontrivial. Nevertheless, it has strong independent plausibility as a thesis about phenomenal states. So the incompatibility of the unity thesis with these views of consciousness should be seen as at least a prima facie argument against these views.

Possibility and explaining the Unity Thesis

If the unity thesis is true, how is its truth to be explained? We do not know the answer to this question. But in this concluding section, we will explore some possibilities. One common strategy is to try to explain unity in functional terms. For example, one might try to explain unity in terms of some sort of informational integration, or in terms of serial processing in the brain, or something along those lines. One obvious problem with this sort of strategy is that it is not clear why this sort of functioning should yield phenomenal unity, as opposed to something like access unity. But an equally deep problem is that for reasons similar to those discussed above, it seems inevitable that this sort of functioning will be present contingently, and that it will be possible for conscious states to exist that do not stand in the relevant functional relations. If so, unity (on these analyses) will obtain only contingently, and the unity thesis will be false. If unity is to obtain necessarily, as the unity thesis suggests, we must look elsewhere. Much of the reason for accepting the truth of the unity thesis comes from the fact that its denial seems to be inconceivable, and perhaps incoherent. This suggests that the unity thesis may be at some level a conceptual truth, although perhaps a deep conceptual truth, whose roots are revealed only by a deep analysis of our concepts. The central concepts involved in the unity thesis are that of a phenomenal state and that of a subject, along with various additional notions such as subsumption, entailment, conjunction, and so on. So one might hope that some light could be shed by attention to the concept of a subject, or by attention to the concept of consciousness. One natural suggestion is that our concept of a subject of experience is somehow premised on unity. For example, one could suggest that ascriptions of subject-hood require as a precondition that subjects correspond to unified phenomenal fields. In the spirit of a sort of bundle theory of the subject, one could argue that we have a prior notion of a phenomenal field, and that we then associate subjects with phenomenal fields. If this is the case, we would expect that every subject would have a unified consciousness. A subject with two distinct phenomenal fields, for example, would be ruled out as a conceptual impossibility: where there are two phenomenal fields, there will automatically be two subjects. How might this work? Our articulation of the notion of a phenomenal field in this paper appeals to subjects and co-instantiation, but one might argue that these can be bypassed. For example, one might appeal to a primitive relation of subsumption (or of co-consciousness) among phenomenal states that makes no presuppositions about subjects of those states, and then define a phenomenal field as a maximal phenomenal state: a phenomenal state that is not subsumed by any other phenomenal state. But even if something like this works, there is a deeper problem. This strategy might explain why distinct phenomenal fields correspond to distinct subjects, but it cannot explain why states of consciousness come packaged into unified phenomenal fields in the first place. For example, nothing in this strategy explains why a phenomenal state cannot be subsumed by two different phenomenal states such that no further phenomenal state subsumes both of these in turn. More generally, nothing here explains why the subsumption relation does not hold in quite unsystematic and fragmented manner. It is possible that an analysis of subsumption itself could do some work: for example, one could argue that subsumption is conceptually akin to a mereological part-whole relation, and so must hold reflexively, antisymmetrically, and transitively, and perhaps in a way that allows no overlap. But this conceptual stipulation does not really make the problem go away. It simply raises the question of why conscious states come packaged as parts and wholes. One might then take a different approach. Instead of focusing on the concept of a subject, one can focus on the concept of consciousness itself. It could be argued that our basic concept of consciousness is not the notion of a simple phenomenal state — what it is like to such-and-such at a time. Rather, our basic notion of consciousness is that of a total phenomenal state: what it is like to be a subject at a time. This yields a holistic rather than an atomistic view of consciousness. On this approach, we do not start with basic atomic states of consciousness, and somehow glue them together into complex states. Rather, we start with a basic total state of consciousness, and then differentiate it into simpler states, and ultimately into atomic states. If this were truly our basic notion of consciousness, then it might explain why the unity thesis is true. On this view, any non-total phenomenal state is derivative on a total phenomenal state that subsmes it. On this view, it is to be expected that any phenomenal states of a subject at a time are all simply aspects of what it is like to be that subject at that time. As such, it is to be expected that for any set of co-instantiated phenomenal states, there will be a subsuming state. On this view, the most basic problem with the theories of consciousness discussed in the last section is that they are atomistic rather than holistic, starting with simple states rather than total states. If this view is right, then any such analysis of consciousness will be a misanalysis from the start. It is not obvious that this sort of conceptual claim on its own yields a substantive unity thesis. But one might tie naturally tie this analysis to a corresponding view of the metaphysics of consciousness. In nature, it may be that the most basic sort of conscious state is the total phenomenal state, or the phenomenal field, or even the phenomenal world. These total states are basic, but they are not featureless: they come with a complex structure from which one can differentiate many aspects. (As an analogy, one can think of a quantum wavefunction, which is a basic state in physics but which nevertheless has a complex structure.) So metaphysically, simple conscious states might be derivative on total conscious states. If so, we would have a clean explanation of why a substantive unity thesis is true. This sort of suggestion is highly speculative, and much needs to be worked out. For example, it is far from obvious that our basic concept of consciousness is that of a total state of consciousness, and one needs to make a direct case for this. And the corresponding metaphysics needs to be worked out in much more depth. But there is at least some plausibility in the idea that the concept of concsiousness, and states of consciousness, are fundamentally holistic rather than atomistic. And this squares well with our intuition that consciousness is necessarily unified. In any case, whether the substantive claims that we have made in this paper are correct or incorrect, we hope to have helped to pin down some of the crucial issues. It is clear that there is much need for further work in analyzing the notion of unity, in assessing the truth of the unity thesis, and in seeking an explanation of its truth. It is likely that such work will be philosophically fruitful.

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