I exposed in The Frequency of Telling Stories what is a denotation of “I” in different contexts, though, what remained constant in that essay, was that I regarded the “I” as being external. I always gave examples where “I” was said by an outer subject or it was me but at a past time or referring the the future. Ultimately I have treated the proper, present “I” and described it in “5.3 The Actual World”:
I define the actual world as being the world in which there is nothing counterfactual and, as I have shown before, every proposition containing qualia implies that I am someone that I am not. Therefore the actual world would be the world in which I’m able to denote precisely the things as I perceive but, as shown, I can’t communicate them to anyone or even myself at a later time. So if you consider the limit of two subjects to their being the same (two very similar people or the same subject after an infinitesimal fraction of time), they would be able to communicate their actual world with qualia. On the other hand the world of ideas, because of its lack of indexicals, would also be a partial description of the actual world.
Here we see that I regarded the actual world as being something I cannot comunicate. I still agree with that idea but I want to give a different argument in order to get to a similar conclusion, this should show how obvious it already was that, in the context I built, there was no space for a definable present proper “I”.
Definability
Similarly as I have seen in Model Theory (Lecture), in order for something to be definable there should be a proposition that satisfies it and nothing else, a remarkable example of the concept is the following: Consider the language of ordered groups Log:=⟨+,>,0⟩ and the ordered group (Q,+,>) . In this case we have no way to define 1, since there is no ϕ∈Log s.t. ϕ(1) is true and false for any other variable.
I want to use here a similar concept of definability, which would then become exactly the same if I would be able to write my theory formally. In particular I should notice that there some sort of propositions that have a free variable and are therefore of the desired kind, but that are true for any inserted variable. For the former example we may for example take ψ(y):=∃yy>x , we notice that whatever we insert in the free variable y it would always be true. Though I see convenience in statin that, a proposition ϕ(x) defines something, only if there is something that it is not defining, therefore ψ(x) would not be a defining proposition. It would be a defining proposition, e.g., in the ordering (Z/(5),>) where ¬ψ(4) holds.
The Subject
When asking whether the subject is definable we must first well specify the language we are speaking in. There may well be different ways to define subjects if we are talking a more externalist language or simply referring to others, though, if we consider the present self, in a completely internalist language, like the one I’m trying to write in [unpublished writings], then one immediately notice that what we mean by subject is including everything that is present in our domain of discourse. Therefore we will find no defining proposition fo subject, since it would hold for any element of our discourse.
Application to Descartes
I regard the Cartesian cogito ergo sum as: from the presence (in my sensations) of any thoughtful activity, it must follow that there is a subject who produced it. And yet, here, i just gave a model where the former sentence can’t turn out to be true, since subject, as shown, is not definable. Two objections come first to my mind: (i) I am not referring to the same subject Descartes is meaning and (ii) the Cartesian claim is then not true, which doesn’t strictly mean to be false. For (i) I need first to state the disclaimer that I have no historical pretence and secondly that I suppose that Descartes wants to denote with subject, either the totality of the res cogitans, for which my argument holds, or the author of such a totality, which would not be part of the domain of discourse and therefore not definable either. For (ii) I would first underline that what Descartes needed is something to be true in any model of our perception, s.t. no sceptical scenario could still both explain our sensations and not satisfy. My scenario though explains all our sensations, by just assuming the presence of such phenomena, and doesn’t satisfy the existence of a subject, therefore I would be enough of a sceptical scenario to falsify the Cartesian claim.