Are the theory wars over? Twenty-five years ago you couldn't cocoa your cappuccino without someone accusing you of floating a signifier, much less close down the, ahem, discourse with a simple "I prefer my coffee that way". Who is this mythic "I", the theorists wanted to know, and how could he presume to know what he prefers? Has he forgotten he's as fictional as Oliver Twist or Mrs Dalloway? Doesn't he know that his likes and dislikes are as ideologically determined as the medium-term financial strategy?

College life these days looks rather less fraught. Theory is on the curriculum, to be sure. But the position you take on it no longer has any connection with your place in the world. Talk about the textual topography of the soul can be handy for seminars on Wuthering Heights, but even the most radically decentred subject must pay back their student loan. So theory won – because nowadays everyone "does" it. But theory lost – because nobody now does any more than "do" it. Like feigning Leavisian aliveness to the felt textures of the organic community, theory has become just another one of those things you affect to believe in in order to make a grade.

Which doesn't mean there was nothing to theory. As Gary Gutting reminds us in this dense but brisk account of the last half-century of what he calls philosophy's "French shenanigans", the likes of Jacques Derrida and Michel Foucault are the cream of the post-war continental intellects. In an age in which more than 40% of schoolchildren end up at "uni", students may like to ponder the fact that back in the 1950s, when the famous structuralists and deconstructionists-to-be were applying to read philosophy at Paris's École Normale Supérieure, a mere 35 people a year cut the metaphysical mustard. Indeed, as Gutting rather ungallantly points out, Foucault failed the entrance exam the first time around – and it took Derrida a full three attempts to get in.

What did they get from their studies? Chiefly, Gutting argues, an Oedipal urge to topple the Sartrean existentialism that had been all the rage since the war. And so, where Sartre talked of the individual's need to remake himself every day in the light of an indifferent or even hostile world, Foucault, Derrida and co professed to see only the indifference and hostility. The idea of man, of the individual consciousness struggling to get a hold on a world external to itself, was just that – an idea. And like all ideas it was a product of language, or, more precisely, language's ability to run rings around its putative users.

Because, so the theory goes, you don't speak language. Language speaks you. You might think of speech or writing as ways of expressing what's on your mind or in your heart but all you're really doing is mouthing the cliches that linguistic structures (and strictures) permit. Marx said man was alienated from his nature. Freud said man was alienated from his desires. But for the post-structuralists, the very idea of man was itself alienating. Had Descartes really had a self, he'd have been kidding it when he said, "I think, therefore I am". "I think, therefore I am being thought" is nearer to the deconstructionist mark. Or as Derrida more famously put it, "There is nothing outside the text".

But was there anything inside the texts of Derrida and his fellow deconstructionists? Gutting is scrupulously fair-minded on this point. On the one hand, he says (in an argument that gives him his title), post-structuralist thought has been no less than an attempt to "think the impossible".

On the other hand, impossible thinking makes for impossible writing, and he boldly admits that "for almost all of us (even those of us who spend a good amount of time on recent French philosophy), [it] cannot be understood through a close, line-by-line reading". Far better, he concludes, to treat this stuff like poetry – as essentially unparaphrasable and never fully explicable.

Fair enough, though I dare say I'm not the only one who finds Foucault and Derrida's coiling, arrhythmic stodge anything but poetic. Kant isn't much fun either, of course, but which of us would deny the certainty-subverting genius of the "first critique"? Rebarbatively obscurantist the post-structuralists may be, but anyone who has read Gary Gutting's fine introduction to their thought will be a little less quick to convict them of charlatanry.

Christopher Bray is working on a history of 1960s culture and politics