I have just had an interesting discussion with people who work on, or in the tradition of, Deleuze. I maintained that Deleuze, and others of that ilk, were wilfully obscure, making it impossible to tell whether there was anything of worth in their works. I also maintained that Sokal and Bricmont did the intellectual community a very great service by writing Intellectual Impostures (American title, Fashionable Nonsense). They exposed the large amount of nonsense, and the gross abuse of science, that are to be found in the work of their targets. Others in the discussion naturally disagreed with me, both on Deleuze and on Sokal and Bricmont.
Even if I am right, that would not exclude the possibility of worthwhile work in response to Deleuze and his ilk. Those who engage with Deleuze may well have worthwhile thoughts of their own, which can then be published and which may deepen our understanding in a variety of fields. Interaction with others often has that effect. Work on Deleuze and his ilk may also contribute to our understanding of intellectual history.
The discussion raised the question of standards of clarity and obscurity. I maintain that some works, such as those of Kant, those of McDowell, and texts in physics, are legitimately challenging by virtue of their subject matter. But others are obscure without good cause. Works by Hegel, Deleuze, Lacan and Derrida are like that.
Such judgements should, however, be supported by some robust and generally acceptable criteria of clarity - although it would be too much to expect that even those who agreed on the criteria, would reach the same conclusion on every difficult book that they considered. I propose two criteria. First, does each sentence make sense? (We cannot expect to get the full sense, or even the correct sense, of a sentence without paying attention to its context; but each sentence should still mean something in isolation.) Second, can I state in my own words what the author has said, listing some specific and worthwhile propositions, and be confident that I have not just invented something that I think he should have said?
The second criterion suggests something that Deleuze scholars might like to do. If they conclude that Deleuze himself said certain things and that those things were worthwhile, they should reflect on whether they have really found those things clearly in the text, or whether they have had to read their own thoughts into the text in order to extract some definite meaning. In particular, could they just have easily have extracted some other, contradictory, meaning? And could they tell when two pieces of writing in the Deleuzian style did contradict each other?