How do I get the idea of my own mind? Do I get it simply by having my mind, or possibly by experiencing the mind I have? Do I perhaps have an “impression” of my mind from which I extract the idea? Here is a problem with this theory: based on my mind alone, I cannot distinguish between it and the world. My mind is my world. The world I know is the world presented to me by my mind, so my world and my mind are coeval and coterminous. The limits of my mind coincide with the limits of my world. When I gaze at my mind all I see is a world. I don’t have an idea of my mind as something in the world. Merely having a mind does not give me a perspective from which I can grasp my mind as an object: I don’t apprehend it as I apprehend the Sun setting on the horizon.
How then do I get the idea? First let us ask how I get the idea of other minds. This idea is useful in social contexts: it enables me to think effectively about the behavior of other people. We probably have this idea innately, as do other mammals. It enables us to think of minds as things existing in the world. But my mind is not included in this general conception; it stands apart from other minds. How do I bring my mind under the conception that includes other minds? Not by thinking of my mind as other! But one thing I can know about other minds is that I am other to them: they think of me as an other mind. So we can imagine the child coming to realize that he or she is an object of thought for other minds: “Oh, so they think of me as I think of them”. Now she is thinking of her mind as something in the world: it is her world but it is also an object in other people’s worlds. She thinks of her mind as being an object for the minds of others. This is the exact opposite of her own perspective on her mind, in which world and mind are merged. She sees herself reflected in the minds of others, and this gives her the idea of her mind as one thing among other things. So we grasp our own mind via our grasp of the minds of others, by understanding that we are objects for them. Our mind cannot give us an idea of itself as existing in a world containing other minds, but our grasp of other minds can give us this idea once we grasp that those minds take us as objects. This is a very sophisticated idea and it is doubtful that other mammals and small children have it. They may have the concept of other minds, but they don’t really have the concept of their own mind. Only by recognizing that other people think about them can they manage to think about themselves, i.e. grasp that they are entities of the same kind as other people. The thought “I have a mind” is really the thought “This world is an object of thought for people with other worlds”—that is, “I exist in other people’s worlds”. My mind and their minds form a totality for me because I think this way: I think of myself from their point of view, because I think of other minds and realize that I am considered by them. No doubt my first thoughts along these lines centered on my mother: “I am an object in my mother’s world, so I must be something in the world as well as a world unto myself”. Then I realize I am an object among others, and am nothing unique (a sobering thought in my childish egotism).
These two thoughts always coexist uneasily: the “I” as object in the world and the “I” as constituting the world for me. Can all this really be just one pinpoint thing in a much larger reality? Thus we oscillate between solipsistic egotism (there is only my world) and vertiginous humility (I am just a tiny speck in a huge wide world). The astonishing thought that I am merely one mind among innumerable others brings together two ways of thinking about the self: the idealist conceit that the world is my world, and the realist concession that the world is much greater than I am. In particular, it locates the self in a world occupied by other equally real selves—as an object of their apprehension. In coming to have the idea of my mind I come to realize that I am much smaller than I thought, even though I know no world larger than the one presented by my mind. The concept of my mind is thus the consummate philosophical concept, because it contains an entire metaphysical outlook on reality, one that generates perplexity and intellectual disharmony. It isn’t just a “faint copy” of a perceptual datum, a “simple idea”. It might even be said that putative possessors of this concept don’t really have it themselves, not fully, because it is just too hard to grasp: I never really understand the idea that I am just one mind among others; my own mind asserts itself too strongly to accept that. I am the world; I am not a minute part of it! Certainly some people never seem to get over the idea that everything centers on them—that nothing else is real (not really real). The idea of one’s own mind as one thing among others is just too lowering, too ontologically disquieting.
In any case, our concept of our own mind is a concept originally derived from our concept of other minds, particularly from the idea that other minds regard my mind as an object in their world. It doesn’t spring from a simple encounter between me and myself, as if my mind introduces itself to me one day and I recognize it for what it is (“Ah, I’ve heard a lot about you, good to meet you at last!”). It arises from complex reflection on the minds of others, an idea with roots in practical biological concerns. Not every being with a mind has a concept of that mind, even those with a concept of other minds.
 Cf. Wittgenstein: “What brings the self into philosophy is the fact that ‘the world is my world’. The philosophical self is not the human being, not the human body, or the human soul, with which psychology deals, but rather the metaphysical subject, the limit of the world—not a part of it”. Tractatus 5.641