For several reasons, then, effective criticism requires the creation of novel theories. To define philosophy in terms of its critical spirit is not, then, to miss its constructive side; it is to require it. It should, of course, be said, that not all philosophers go in for criticism and construction in equal proportions. Some-perhaps Russell-do; some-such as Nietzsche- are more knockers-down than standers-up; and some of the great system-builders-perhaps, Spinoza-are more standers-up than knockers-down. As ever with work, there may be a certain division of labour-just as there are theoreticians and experimentalists in physics. Moreover, some philosophers may well be more interested, subjectively, in constructing their own system of thought than in using it to criticise others-just as some theoretical physicists may be more interested, subjectively, in developing the mathematics of their own theory than in putting it to the test. So it can look as though creating systems of thought is an independent part of the philosophical enterprise. But if the argument I have just given is right, it is not. Objectively, its existence is a corollary of the critical nature of philosophy.--Graham Priest (2006) "What is Philosophy" (p. 206).
For Priest, philosophy is a "critical spirit;" it "is precisely that intellectual inquiry in which anything is open to critical challenge and scrutiny." (202) In her famous (2013) response to, and elaboration of, Priest (not just Priest), Kristie Dotson points out that on Priest's view, philosophy is 1) subversive, 2) unsettling, and 3) of universal import (Priest 2006, 202-203). As the first sentence above makes clear, Priest relies on a distinction between effective and (let's say) not-so-effective criticism. Unfortunately, he does not quite explain what he means by it, but from his use we can infer some of the things he he has in mind.
One sense is intellectual (and this is the one that Priest emphasizes): the criticism becomes more (i) intelligible/sensible and even (ii) visible in light of alternative theory (206). To become intelligible and visible are not the same, and Priest does not treat them as such. This does not exhaust the uses of alternative theories in making criticisms effective. But here I just want to note also the sociological sense: (iii) to offer effective criticism means one cannot be ignored. So, if one cannot produce a rival theory one's criticism is ineffective (one may as well keep quiet). Priest does not really discuss this sociological feature, but it hovers in the background because Priest motivates his account through copious and generous quotation of Kuhn's (and Laudan's) philosophy of science (recall this post). That is, the inability to produce a constructive, rival theory is a stepping stone to the silencing or making ineffective of one's criticism. (Obviously, Dotson alerted me to the significance of this.)
As an aside, it is worth noting that Priest seems to imply that effective criticism with older/discarded/unfashionable theories is also not effective. I suspect, but can't prove, that this, too, is a sociological claim. It presumably relies on the idea that old theories were discarded for good reasons and so can't really be revived. (There is, here, then, a kind of rationality assumption akin to efficient market in ideas about the institute of philosophy; the community rejects/discards theories for solid, in the sense of durable, epistemic reason.)
Now, I don't wish to imply that Priest (the philosopher) is especially keen on silencing folk. His work is notable for its ecumenical, inclusive spirit. (The inaugural lecture I am quoting from has a serious engagement with Derrida's views.) But the demand that a criticism has to be couched in a rival theory has the effective effect of making most criticisms impotent. Of course, Priest would allow that in a colloquium talk (during Q&A) or in a seminar one could raise criticisms without absent a novel theory. (He is very good on the norms that govern such settings.)*
The position also makes it much harder to permit reductio as a legitimate form of philosophy if one ends up in skeptical aporia. This anti-skeptical sensibility is quite clear in his criticisms of Rorty's Derrida:
Are Derrida and Rorty playing with us? I doubt it; but if they are, we have no reason to take them seriously, any more than I have to take seriously the things that you tell me if you area musing me with riddles-'As I was going to St. Ives, I met a man with seven wives ...' This is, in fact, just a special case of a well-known bind that was first observed as long ago as Plato's Theaetetus (171a4-c7). Someone who claims that there is no appropriate notion of truth to which assertion must answer can say anything they like. There is therefore no reason to believe them. They have argued themselves out of the game. (200)
I leave aside here, Priest's rejection of play (recall this post; or Derrida's category of frivolity). But it is not quite right (I was about to say 'true') that "Someone who claims that there is no appropriate notion of truth to which assertion must answer can say anything they like." That really depends on their conception of responsible speech. (And here one may well think there are crucial differences between Rorty and Derrida.) So, for example, if you know that somebody's conception of speech is ethical -- that they care about the prevention of harms, that they recognize the capacity of language to be itself a source of oppression, that they think their words create and bind their selves --, one may well have excellent reason to find their utterances trustworthy (I almost said 'believable' and 'credible') despite the fact that they are disinclined to invoke truth. This may well require contextual and contrastive judgments of character; of course, such judgments may be inefficient or themselves corrupted.
Either way, Priest's rejection of Derrida is too greedy here, even if it is sociologically effective. Most of Priest's readers will come to his text already agreeing with him that Derrida is not worth taking seriously (even if Priest clearly thinks otherwise). As Dotson implies, once one recognizes that there may be more than one game in town, we may also pay more attention to how the rules of the game we're playing may rule out moves on grounds that narrow the playing field too (ahh) narrowly.
*One is inclined to suggest that on Priest's tacit model of philosophy, seminars and colloquia are the context of discovery, and so what he calls the 'critical spirit' is given widest latitude.