As against my understanding of hallucination, it could be said that one of the things which hallucination at least often-times shares with perception is a sense of the presence of the hallucinated or perceived object. But an anticipation by itself hardly constitutes a sense of presence. So don't we need to add something to unrelinquished anticipation to arrive at the sense of presence which hallucination shares with perception? Perhaps what we need to add is - heaven forbid - an inner image! It is, perhaps, the image which at least is 'present to the mind'. And perhaps such an image is also, in its way, the fulfilment of the anticipation.
So, we do sometimes talk about 'sensing the presence' of something or someone; we may even talk about sensing 'a presence', 'presence' now being another term for ghost or spirit. I suggest that the logic of this talk of 'presence' is best understood by comparison with our talk of déjà vu. An experience of déjà vu is properly articulated with a phrase like 'it is for me just like I had already experienced this very same thing happening.' Such uses of words defines the experience in question. However we have gazillions of experiences every day which we have had before - walking down the same corridor to our office, using the same toilet, drinking from the same coffee cup - and these precisely do not engender an experience of déjà vu. So in a sense the experience of déjà vu is precisely not like an ordinary experience of encountering something again. What this goes to show, I think, is that we are here using the phrase 'as if I had already had this experience' in what Wittgenstein called a special 'secondary sense'. We are drawn to use just this phrase; that we are so drawn is criterial for the experience in question; yet the use is not to be taken as justified by the current experience having something in common with the perfectly ordinary experience of encountering something which one had previously encountered in just the same way. (It is neither justified nor unjustified; that's just not how it works.)
What I am claiming is that the ordinary use of 'sense of presence' is, just like that of déjà vu, a secondary sense application of the term. We precisely do not mark with it something which is shared by both hallucination and perception. But perhaps, the objection goes, this is not the sense of 'sense of presence' which is relevant here. Sure, there is such a sense which applies specifically to hallucination, but what is relevant here is rather the (...alleged...) sense that (...allegedly...) applies to the case of the perception of objects. When I ordinarily see an object I ordinarily have a sense of the presence of the object (...so the argument goes....). And this same sense of presence can obtain in at least some hallucinations. Thus one might use, in both hallucinatory and perceptual cases, sentences like 'It is for me just as if I were actually seeing the cat' to emphasise the same point.
As against this I want to ask just what is meant here by a 'sense of presence' in the non-hallucinatory case. For example, does the person who says that when I actually see a cat I have a sense of the presence of a cat mean more by this than that they are, er, seeing a cat? If so, what? I see a cat and in seeing this cat most often can also be said to see that there is a cat there on the mat. This however is precisely not shared with hallucination: when I hallucinate a cat I precisely do not see that there is a cat there on the mat. ('Seeing' and 'Seeing that something is there' are what we call success verbs/clauses. Hallucination is not successful or unsuccessful seeing!) Or is it that when someone sees a cat and hallucinates a cat it can seem to them that they see a cat? Is the 'sense of presence' a 'seeming' of some kind? But then, well, honestly, it is rather hard to know what is being done with the phrase 'it seems to me that I see a cat' when used by someone who straightforwardly, in a situation which wasn't anticipated by them to be one of deception (for we do use it as an expression of hesitancy when we're not sure if we should believe what we see, even when we are in fact undeceived), does see a cat. The concepts of appearance (seeming, etc.) gain their sense in virtue of the distinction they draw between the case of the seeming and the case of what is.
Now, it may be that there is some use being envisaged for 'sense of presence' which has not yet been spelled out. A use which is shared by both hallucinatory and perceptual cases. I however have not had it introduced to me, nor have I yet been able to pull it out of my own noggin. So, well... I'm waiting.
What however is also interesting to me is that we do use this notion of a 'sense of presence' to describe cases of hallucination. I think it is worth pondering why this should be. (And when we think on the 'why' here I think we should make sure that we don't automatically start to look for a justifying reason, rather than an elucidatory cause, for our talk.)
On my understanding of hallucination it involves a form of anticipation of right now perceiving something which is unrelinquished despite the fact that one also has no experience of this anticipation being confirmed. Despite, that is, one not perceiving whatever is presently anticipated. This leads us to use the word 'presence' in the spooky, secondary sense, manner. 'I sensed the presence of my dead grandma' or 'I felt her presence' is what we are spontaneously drawn say. Despite her manifestly not being present: if she were actually present then we precisely wouldn't have that experience which we call the 'experience of her presence'. So, my question is: why are we drawn to use this locution? I take it that the question is the same as that which attends the use of 'déjà vu': why do we use this phrase to describe an experience which is precisely not like the gazillions of experiences we have everyday for the second or third or millionth time?
Well, the reason (in the sense of cause that moves us, not in the sense of that which I could give as my reason) why we use the notion of 'presence' is, I think, because we have here to do with an unrelinquished anticipation. In this way it, the hallucination, is similar to a fulfilled anticipation (i.e. to a perception) since in the hallucinatory case there is no cancelling of the anticipation despite the manifest absence of what is anticipated. And in the perceptual case it is also not cancelled since it is instead fulfilled, and now has its life immanently within the perception itself. In short, this is what both perception and hallucination have in common: the continued life of the bodily anticipation.
Similarly with déjà vu. It is not really that I seem to remember having had this conversation or visual experience before. We've all done that, all the time, and it doesn't amount to déjà vu. We don't reach for that description because it is part of the content of the experience; we are not justified, not even seemingly, in using the 'as if I've done this before' locution. Something in the temporal structure of the experience has instead gone awry. Something like the registering of the newness of each experience through time has failed, thereby constituting a distinctive dissociation. We want to say something like 'It is as if this very stretch of experience - not simply its content, but it in its temporally individuated identity - had happened before.' But that of course is nonsense, since what it is for the experience to be this one, when we are thinking not about its content but about its temporally indexed identity, is precisely for it to not be any previous experience. And yet we want to say what we say, and that we want to say just this is criterial for the experience being what it is. It's notable that with both déjà vu and hallucination we necessarily encounter a form of dissociation or trance or loss of reality contact - not necessarily any global state of such within the individual, but within the experience itself, as an essential part of its form.