We cannot say of the purloined letter that, like other objects, it must be or not be somewhere but rather that, unlike them, it will be and will not be where it is wherever it goes.
If what Freud discovered, and rediscovers ever more abruptly, has a meaning, it is that the signifier’s displacement determines subjects’ acts, destiny, refusals, blindnesses, success, and fate, regardless of their innate gifts and instruction, and irregardless of their character or sex; and that everything pertaining to the psychological pregiven follows willy-nilly the signifier’s train, like weapons and baggage.
Here we are, in fact, once again at the crossroads at which we had left our drama and its round with the question of the way in which the subjects relay each other in it. My apologue is designed to show that it is the letter and its detour which governs their entrances and roles. While the letter may be en souffrance, they are the ones who shall suffer from it. By passing beneath its shadow, they become its reflection. By coming into the letter’s possession —an admirably ambiguous bit of language— its meaning possesses them.
Lacan’s seminar on “The Purloined Letter”, Ecrits