Three philosophers kick off a five-page look at Derrida's legacy with thoughts on how he transformed the customs and practices of a discipline.

I am ambivalent about not having been in Cambridge during l'affaire Derrida in 1992. It meant missing the delicious pleasures of a full-scale academic row, but also avoiding getting covered with a fair amount of spittle. I tended to think of Derrida as a poor candidate for an honorary doctorate. I relished the irony that he was eventually given this degree in the same ceremony as Geoffrey Elton, praised for his passionate defence of truth and objectivity in history. I didn't, however, froth whenever Derrida was mentioned. But, then, I had never belonged to a university where the hey-nonny-nonny pomo tendency had tried to elbow out decent philosophy.

We have to be careful interpreting different academic styles.

Suppose someone announces that Scotland is a social construction. Before exploding that nobody built Ben Nevis, we might ask for a little context and charity. Perhaps the idea is that Scottish traditions, or what it means to be Scottish, are creatures of invention and myth. The kilt was invented by an English industrialist, and there never were clan tartans. When we hear of the death of the author, before sneering that things such as Middlemarch don't grow on trees, is a point being made about the way writers are embedded willy-nilly in a culture or language? When we hear of meaning lying forever in the mind of the reader, before responding contemptuously that when a sign says "speed bump" the next thing you come upon is a speed bump, we might wonder whether a quite sensible, if limited, point is being made about the endless interpretations that slightly more interesting texts invite.

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Probably, this charity does not extend to all philosophers who have entangled themselves in confusions about signifiers and what is signified.

There may be people out there who say they cannot distinguish between the sign and the bump or who confine themselves to theorising about the sign.

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They might do good work, comparing "bump" as it occurs at the roadside with "bump" as it occurs in "goose bumps" or as a name for the cry of the bittern. The hey-nonny-nonny tendency may playfully, if pointlessly, reflect that the word contains the highly charged subset of letters "bum".

Again, harmless, provided they do not draw a salary for it and remember that if they hit the roof of the car, it will be the bump that caused it, and neither a bum nor a sign. As for interpretation lying endlessly in the mind of the beholder, well, there is such a thing as learning to read and if you haven't done it properly, the roof of the car will be more of a threat.

Deconstruction itself need not be the nihilistic, destructive bogey it is usually taken to be. It is not a bad idea to wonder whether the overt message of a text is as consistent as the author might have hoped or whether, somewhere, there may be signs of complex undercurrents. It cannot be a bad thing for which to be on the alert, although you will not always find it. "Speed bump" contains no hidden signifier of flatness. The difficulty is to maintain both excitement and intelligibility. The points about Scotland, or Middlemarch , or the vistas of interpretation, or deconstruction, are neither very exciting nor very new. The advice to look out for a self-undermining moment is as old as Plato, for instance.

Anyway this can only be the beginning of any serious work. If you really want to press home the idea that an author's point is undermined by the language used in presenting it, you have to make the charge stick. It takes work to decide whether a sonnet betrays insincerity, for example. The excitement that surrounded Derrida often seemed to be premised on the thought that something called Theory enabled you to avoid the hard work, and effortlessly attain some vantage point from which the Western novel, or Western philosophy, or patriarchal science, or whatever the next target might be, could be diagnosed as just another self-undermining discourse or narrative. This is of course an attitude especially appealing to the young, and I think much of the heat of l'affaire Derrida came from the indignation of those who thought, rightly, that mockery and ignorance need taking down a peg, and that universities are a good place to do it. Seen like this, Derrida or his disciples are like mentors encouraging people not to read.

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And, alas, many in the world, whether ideologues in the White House, or similar fundamentalists in Arabia, have found that a highly congenial lesson to absorb.

Hostility to this adolescent attitude also explains an apparent paradox that defenders of postmodernism often seize on. This is that their opponents, careful academics, managed in one breath to say both that Derrida's works were gibberish, and that they represented a dire threat to Western civilisation. The paradox is only superficial, though. Some gibberish - Lewis Carroll comes to mind - emanates not contempt but affection for its targets. But postmodernist gibberish does not. Out from the confusion comes a distinct whiff of the complacency and superiority that come from having seen through something by which the vulgar are taken in.

Derrida's defenders say that while some socks in the same drawer, such as Foucault or Rorty, may emit this aroma, Derrida himself is the most modest, scrupulous and attentive reader. I do not know whether this is true. He may deserve some credit for trying, but probably less for succeeding. Whether his intention was serious scholarship (and who believes in intentions any more?), his practice encouraged mainly mockery. John Stuart Mill thought that in the market of ideas, truth would prevail. I don't think he was right. I think it is a political and social achievement to enable truth to prevail. The first thing to establish is that it is possible, the second to establish that it matters, and there is more to be done after that. I don't think we should honour an attitude that makes those tasks harder than they already are.

Simon Blackburn is professor of philosophy at Cambridge University.

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