Dr. Mary Klages summarizes Lacan's 3 stages of development (Real, Imaginary, Symbolic):

"So, to summarize. Lacan's theory starts with the idea of the Real; this is the union with the mother's body, which is a state of nature, and must be broken up in order to build culture. Once you move out of the Real, you can never get back, but you always want to. This is the first idea of an irretrievable loss or lack.

Next comes the Mirror stage, which constitutes the Imaginary. Here you grasp the idea of others, and begin to understand Otherness as a concept or a structuring principle, and thus begin to formulate a notion of "self". This "self" (as seen in the mirror) is in fact an other, but you misrecognize it as you, and call it "self." (Or, in non-theory language, you look in the mirror and say "hey, that's me." But it's not--it's just an image).

This sense of self, and its relation to others and to Other, sets you up to take up a position in the Symbolic order, in language. Such a position allows you to say "I", to be a speaking subject. "I" (and all other words) have a stable meaning because they are fixed, or anchored, by the Other/Phallus/Name-of-the-Father/Law, which is the center of the Symbolic, the center of language.

In taking up a position in the Symbolic, you enter through a gender-marked doorway; the position for girls is different than the position for boys. Boys are closer to the Phallus than girls, but no one is or has the Phallus--it's the center. Your position in the Symbolic, like the position of all other signifying elements (signifiers) is fixed by the Phallus; unlike the unconscious, the chains of signifiers in the Symbolic don't circulate and slide endlessly because the Phallus limits play.

Paradoxically--as if all this wasn't bad enough!--the Phallus and the Real are pretty similar. Both are places where things are whole, complete, full, unified, where there's no lack, or Lack. Both are places that are inaccessible to the human subject-in-language. But they are also opposite: the Real is the maternal, the ground from which we spring, the nature we have to separate from in order to have culture; the Phallus is the idea of the Father, the patriarchal order of culture, the ultimate idea of culture, the position which rules everything in the world."