What is the reach of philosophical argument? (De Rose/Lewis/Hume...)

Our very own Helen de Cruz called my attention to this fascinating post by Keith DeRose. Consider his claim [A]:

[A] But as it generally goes with philosophical arguments, they don't produce knowledge of their controversial conclusions about substantive philosophical matters.--DeRose.

Initially I thought that in [A] DeRose was relying on a claim about the nature of philosophical argument; let's call it "a no knowledge producing property of philosophical argument." This has a Humean flavor to it. I was (unintentionally, perhaps) led in this hermeneutic direction by DeRose's quote [B] from David Lewis' (1996) "Elusive Knowledge:"

[B] We have all sorts of everyday knowledge, and we have it in abundance. To doubt that would be absurd. At any rate, to doubt it in any serious and lasting way would be absurd; and even philosophical and temporary doubt, under the influence of argument, is more than a little peculiar. It is a Moorean fact that we know a lot.

However, in [B] Lewis is not endorsing a no knowledge producing property of philosophical argument. All Lewis is observing is [i] that Moorean facts are not really undermined by philosophical argument and that, in opposition to Moorean facts philosophical argument has a not-so-serious (frivolous?) and un-enduring impact. That is, [ii], Lewis is claiming we can't really be skeptical about Moorean facts. This [ii] might be a claim in empirical psychology. But Lewis also offers a further argument for [i], namely, "It is one of those things that we know better than we know the premises of any philosophical argument to the contrary." So, Lewis may well think that when it comes to matters other than Moorean facts, philosophical argument may have quite an impact. I happen to think that Lewis's claim that it is  "a Moorean fact that we know a lot," is way too greedy, but that's for another day. 

In [B] Lewis is (perhaps unconsciously) echoing a (once-famous) footnote [C] by Hume:

[C] all his [that is, "Dr. Berkley's"--ES] arguments, though otherwise intended, are, in reality, merely sceptical, appears from this, that they admit of no answer and produce no conviction. Their only effect is to cause that momentary amazement and irresolution and confusion, which is the result of scepticism.--Enquiry Concerning Humean Understanding [Hume's italics--.]

Leaving aside Hume's  diagnosis of the status of Berkeley's arguments, Hume's is also not endorsing a no knowledge producing property of philosophical argument. Hume's position allows that many arguments can produce conviction (including those that he takes to be very bad arguments). In [C] Hume is diagnosing a general feature of arguments that have skeptical consequences (not just about Moorean facts): their "only effect is to cause that momentary amazement and irresolution and confusion." In various places Hume suggests that it simply is not in our nature to remain hung up over skeptical consequences. (This undeniable interpretive fact has generated, alas, the so-called "New Hume," interpretation.)

Okay, let's return to DeRose's piece. There is evidence that DeRose may be committed to the no knowledge producing property of philosophical argument. For at some point he asserts that:

[D] Some of these arguments are relatively good at accomplishing what philosophical arguments generally do, and, in particular, some of them are successful at showing how someone might reasonably believe the conclusions of the arguments.--DeRose

[D] seems to imply that (valid?) philosophical arguments can produce reasonable belief about the conclusions of arguments, but presumably reasonable belief falls short of knowledge. Now, as I was wondering why DeRose would think sound arguments would share in the general "limitation" of philosophical argument, it occurred to me that one could read [A] differently. Recall:

[A] But as it generally goes with philosophical arguments, they don't produce knowledge of their controversial conclusions about substantive philosophical matters.--DeRose.

One could also see this as a claim about philosophy. In fact, DeRose signals this with that ugly locution "substantive philosophical matters," implying that there are also trivial philosophical matters. Now, not unlike Hume or Derrida, I take the frivolous very seriously in philosophy. But DeRose does not strike me as that kind of philosopher. (I am no expert on DeRose's views having read only a few famous articles.)

Rather in [A] he seems to be embracing a conception of (the really serious stuff in) philosophy as essentially contested. There is very good evidence that DeRose endorses this:

[E] Philosophy is wonderful--and in large part precisely because it deals with questions where we can't yet know what is right. (I think there's something to the idea that once we get to the point that philosophy is producing actual knowledge about a topic, then the area of philosophy that deals with the area is likely to break off and no longer be thought of as philosophy.)

Elsewhere, I have argued against the thought that all the break-aways from philosophy (fill in your favorite example: psychology, economics, political science, history, etc.) either have "actual knowledge" or -- even if granted that they do possess "actual knowledge" -- are philosophy-free in all the relevant senses subsequent the split (even physics has plenty of philosophy left).  But I have to admit that I am rather pleased that a major epistemologist embraces the idea that in philosophy we really do not expect to get it right, even thought we might not give up on the regulative idea or the useful, almost Kuhnian myth that one day we might know and produce breakaways. 

So, after reflection, despite my aesthetic dissatisfaction about [A], [A] now strikes me as the first step to wisdom--if not wisdom as such, then certainly wisdom about philosophy. We should be grateful to DeRose's generosity for sharing it with us.