The appetite for conclusive explanation has always been provoked by certain kinds of art - as the recent correspondence in this paper about the "true" meaning of Waiting for Godot reminds us. Earlier this week, one reader advanced the highly ingenious theory that Godot should actually be read as "Go. Dot", in other words "Go. Full stop", the moral instruction of the play presumably being that movement in any direction is better than paralysis. Others talked of obscure French cyclists, Resistance fighters, Balzac characters and concealed homophones (God / Eau). This itchy compulsion to elucidate isn't exactly a mystery itself, of course. Enigmas do not suit our contemporary habits of mind; they are an affront to a culture of transparent meaning. But the impulse to explain arises, I think, out of a misapprehension - because all art is in some sense a coded message, it is an understandable, though false, assumption that there must be a single clear-text solution to that code. Even in works that are calculatedly ambiguous, the conviction that there is a privileged reading that has dominion over all others is difficult to dislodge.

Writers, including Beckett, can sometimes be mischievous about exciting this sense of a tantalisingly elusive clarity. Waiting for Godot, Beckett noted, would be perfectly comprehensible to anyone who managed to read it attentively, an instruction that has probably resulted in some hapless sap anagrammatising every other line in the search for secret messages. Martin Amis did something similar when he published his novel Other People - subtitling it "A Mystery Story" and announcing in interviews that its apparent opacities had a simple explanation. Julian Barnes, he said, had "got it" first time but others might have to read the novel twice to solve the puzzle. As a way of securing a certain knotted attention from your readers, this could hardly be improved upon and, for a time at least, there was a vigorous exchange of theories about how best to solve the mystery.

Nor is it just good art that provokes the audience in this way. Dennis Potter's last two television plays have generated a similar, if smaller, cottage industry of exegesis, because for the compulsive decoder there is no such thing as a loose end. That dangling thread is just as likely to be the handle to a trap-door, which, pulled open, will reveal a concealed chamber within the work. Authorial forgetfulness, waning powers, the hurried rush to beat death to the final page? Don't be so naive. Again, Potter has encouraged the process, filling both plays with sly allusions that hint at hidden treasure and I confess that I am guilty of code-breaking myself, arguing in one review that the name of the main character in Cold Lazarus, Emma Porlock, was a not-very-covert acknowledgement by Potter that this was his "Kubla Khan", a morphine dream set down in a moment of dazed inspiration.

Some of my correspondents have dug a little deeper: "Am I one of the few people who has picked up the message in Dennis Potter's Karaoke and Cold Lazarus?" writes Mr Robinson, noting that both plays end with the murder of the villain and that Potter joked in his final interview about shooting Rupert Murdoch. The plays, Mr Robinson suggests, may be a deliberate incitement to media terrorism. It wouldn't be beyond Potter, certainly, though you would have thought he could have come up with a less risible acronym for his secret army than RON - hardly an aid to recruitment.

Mary Rensten has another suggestion: "I wonder if I am alone," she writes, "in seeing another allusion... in the naming of his hero Feeld. Are we to interpret this as Potter's Feeld, or rather Potter's Field, a public burying place?" As it happens, she has company - Alex Burns advances a similar theory in the Evening Standard: "Has anyone else noticed that the writer in both plays is named Feeld. So Potter-is-Feeld and traditionally Potter's Field is the burial place of those who have failed, right? I wonder what other barbs may be buried in these texts?" he continues, unleashing the verbal metal detectors on that uneven terrain.

Alert decoders will have noticed a common theme in all these letters - the almost formulaic inquiry as to whether the writers have company in their conjecture - "Am I alone?", "Has anyone else noticed?" and so on. This speaks to the other fascination of gnomic texts, the promise they hold out of a kind of intellectual VIP lounge, accessible only to those who have worked out the password. The mass of the audience will be content to remain passive consumers, but some will attempt to penetrate backstage, to discover the tricks that animate the performance. But it may be that there is no secret room, in either good or bad art - that the struggle for comprehension by readers is itself the meaning of a great impenetrable work, and a charity we confer on those that are merely empty.