It has often been observed that there is something funny about “I” referentially speaking yet we use it all the time. I would say that we don’t know what we are referring to: we don’t know what the self is. This is an old story: philosophers have had a difficult time saying what the self is, even to the point of having no satisfactory word for it. People used to speak of the “spirit” and the “soul”, but this is now deemed suspect and spooky; today we prefer “person”, “subject”, or just “self”. None of this verbiage provides any clue as to what we are talking about, however. Is the referent of “I” a body, a brain, a part of a brain, a center of consciousness, a sequence of connected mental states, a primitive person, or nothing at all? The self is a mystery: we don’t know what it is. Yet we talk about it all the time (and think about it too)—the word “I” is always on our lips. You might think that we could define the self as “the bearer of conscious states”, but what is this bearer—is it a body or a brain or a center of consciousness, etc.? Given our ignorance of what it is, shouldn’t it be difficult to refer to it successfully? Some have said that we are acquainted with the self, as we are acquainted with pain or the color red; but if so, it is an acquaintance that provides no illumination as to what we are referring to. Do we introspect the self? Apparently not, as Hume famously observed. True, we know that it exists (at a given moment anyway): the Cogito supplies us with grounds for a bare existential claim. But this is cold comfort given that we don’t know what it is that so indubitably exists. Descartes thought he knew that the self is a thinking thing at least, but again that doesn’t settle what kind of thinking thing—it could be a brain or an immaterial substance or just a loose conglomeration of ideas. Still we happily bandy the word “I” about, as if we grasp clearly what it is that we are designating. We even have a semantics for it (content and character and all that); we just don’t know what kind of entity “I” refers to. The self is just whatever it is that “I” refers to. By contrast, we don’t think that pain is just whatever it is that “pain” refers to: we know quite well what pain is. The self is a stark enigma. 
It is often supposed that this is a peculiarity of the first-person pronoun, but that is not true. The same point applies to the other personal pronouns: “you”, “he”, “she”, “they” etc.: in each case we are referring to entities whose nature eludes us—the very entities that use ”I” to refer to themselves. I don’t know what I am and I don’t know what you are, or her over there. I don’t even know what it is when I refer to my pet lizard’s self with that demeaning pronoun. All these are words we use to talk about things whose nature we don’t grasp; and I don’t mean we don’t grasp this nature deeply—I mean we really don’t know what kind of thing we mean when we use these words. In a clear sense, we don’t know what it means to say “I am hot” or “She is smart” or “You are funny”. Do we really understand these sentences? True, they have a use, but that is all they have–they have no clear ontological content. No proposition is intelligibly conveyed by them, since we don’t know what the subject of the proposition is. Whatever meaning they have, it doesn’t convey the nature of the thing denoted. The sense is not a mode of presentation of the reference, if that means it enables the speaker or hearer to grasp what kind of thing is denoted. Since these expressions are at the heart of ordinary language use, we can say that our grasp of meaning falls far short of knowledge of the reference of some of our most common expressions. The mystery of the self thus infects linguistic understanding, rendering it at best partial. We are like people referring to colors but who have never seen any: such people would refer to things whose nature they don’t grasp. We know about things that are closely associated with selves, namely mental states, but the self itself is an unknown quantity—an I-know-not-what. Reference to the self thus proceeds in the absence of knowledge of the referent (though of course we know many things about selves).
Why don’t we know the nature of the self? What is it about the self that precludes knowledge of its nature? I don’t think we know the answer to that question either; indeed, our ignorance seems distinctly odd considering how close we are to our own self (it isn’t as if selves exist on the far side of the moon). We ought to know the self much more intimately, but in fact we have to admit epistemic defeat in the face of the self: nothing in our self-knowledge reveals the kind of thing that the self is. The personal pronouns seem merely to point without specifying what kind of target they are pointing at. They operate in such a way as to compensate for our natural ignorance of the self rather than to express our knowledge of the self (as many acts of reference do). I think their peculiar semantic character should receive more attention. 
 It would be wrong to suppose that our ignorance of the self is like other sorts of philosophical ignorance such as not knowing the correct analysis of knowledge, or the metaphysical status of color, or whether “good” expresses a primitive property. Our ignorance of the self is far more radical than that: we really don’t know what order of thing we are dealing with. Hume was right: we have no concept of the self such that its general nature is revealed by that concept. This is why a person unlettered in philosophy can be made quickly to accept that he or she is ignorant about what a self is. This is ground-floor ignorance, not ignorance of high-flown philosophy. Compare color: a blind person is far more ignorant of color than a sighted theorist trying to come up with the right analysis of color. Similarly, our access to the self reveals almost nothing about what kind of thing it is: we are effectively self-blind (though self-obsessed).
 The connection between meaning and knowledge has been explored but not the connection between meaning and ignorance—ignorance of a very basic sort. Somehow language had to cope with the deep-seated ignorance we labor under in the case of the self, and it came up with the apparatus of personal pronouns (and associated expressions). It converted deep ignorance into a viable system of reference. How did that happen? How did language manage to latch onto selves in an epistemic vacuum?