or, is it ever possible that the letter does not arrive at its destination?
There is a well-known debate between Lacan and Derrida. It is, for instance, a debate that Althusser alludes to in his Writings on Psychoanalysis: Freud and Lacan [New York: Columbia University Press, 1996]--an essential reading in understanding why psychoanalysis is important for Marxism. I am not sure if the debate really materialized in these terms but Lacan does acknowledge, in one of his Seminars (XX), the presence of a Derridean critique of his Ecrits: Jean Luc-Nancy and Philip Lacoue-Labarthe's The Title of the Letter [Albany: SUNY Press, 1992]. This book is a very lucid Derridean critique where the authors claim that Lacan's anti-philosophical gesture, the ex-centring of the Subject (as the Cogito), is actually a reinscription of the philosophical subject--even if the subject of psychoanalysis (unlike the subject of the traditional philosophical discourse) is a lacking subject.
Now, the real question is not so much if the subject is lacking or not. In fact, Lacan's formula has always been "failure to be" ("manque a etre"). In other words, the subject in psychoanalysis is not a subject who lacks, but rather a subject who fails. The two are different. In the first formulation, there is a subject and then there is a lack. In other words, the phrasing posits the existence of a subject and then identifies its status as the one who lacks. Whereas in the second formulation, the very existence of subject is in question: failing subject, failure to be a subject... I think the Lacanian response to the Western philosophical discourse is to introduce a crack, a suspicion, a question mark. Or, to speak graphically, to strike the S of the subject with a bar. In other words, the subject in psychoanalysis is a split subject not a lacking subject. The Derridean critique would be correct only if Lacan was speaking of a subject who lacks, as opposed to a failing subject.
But, then, is there no debate between Lacan and Derrida? There is and it begins with Lacan's rather controversial (not the first time) formulation: "A letter always arrives at its destination." Derrida's response in The Post Card: From Socrates to Freud and Beyond [Chicago: University Of Chicago Press, 1987], as paraphrased by Althusser, is "It happens that a letter may not arrive at its destination." Given this set up, it may be quite tempting to "interpret" Lacan as the (obscene) Father of necessitarian teleologists and Derrida as the (good) shaman of the radical contingency. Nevertheless, I strongly believe that we should resist this temptation.
We should resist the temptation, because the debate is on the ontological status of surprise (recognition/misrecognition) and about how to understand temporality. To begin with, neither formula is incorrect. Viewed from the perspective of linear temporality and the humanist conception of intentionality, it does happen that the letter (understood in its multiple meanings, as a letter in an envelope, as a letter of the alphabet, as the capital letter of a particular word, etc.) may not arrive at its destination. In fact, it is always a surprise when it arrives at its destination.
Yet, on the other hand, viewed from the psychoanalytical perspective of temporality--and here I am referring to Freud's concept of nachtraglichkeit/apres-coup/after-effect--a letter always arrives at its destination because its destination is always posited after its arrival. To put it differently, from a psychoanalytical perspective, there is no destination of the letter that pre-dates (no puns intended) its arrival. In this formulation, Lacan articulates the circular logic of performativity of the letter: There is no real surprise because everything is a surprise. And in fact, if there is a surprise it is always in relation to the fantasy of a pre-destination. When we subtract the concept of pre-destination as an ontological entry point (as we should subtract the concept of subject as an ontological entry point too) it will become possible to glimpse at the temporal moebius strip that the Lacanian formula points at: If the letter is performative and if the last signifier reconfigures the entire chain that preceeds it, if the destination is also where the letter arrives at, then a letter always arrives at its destination-with the proviso that the meanings of "arrival" and "destination" are understood within the non-linear world of the split subjects.