Is it a duck or a rabbit? (Is it edible?)
Wittgenstein's use of the duck-rabbit to illuminate the idea of 'seeing-as' popped back into my head after another one of those slugging matches in a combox.
One of the problems in asserting the importance of a natural law perspective on morality, or more broadly, the importance of philosophy and reason in religion, is that you are faced with the inevitable fact that you can't usually convince people. So, in my last outing, however many cogent arguments I can put against consequentialism as a moral approach, I didn't end up convincing my opponent. (It's in the combox here in the Catholic Herald if you can be bothered.)
The temptation here goes one of two ways. First, there is fideism. If natural reason doesn't work, it's because the idea of a reason detached from revelation is incoherent. (It's an issue that occurs regularly in Ed Feser's blog, its last outing here.) Second, there is New Atheist rationalism: 'if you can't prove I'm wrong, that's because you're a sky-fairy-worshipping-irrationalist and I'm not.'
Now, fideism has at least one thing right. Without revelation, we cannot attain full knowledge, either because (as in our supernatural end of the Beatific Vision) we can't know about it unless we're told; or (as in understanding our natural end of virtuous living in this life) we're liable to go wrong due to our imperfections. So it's perfectly true that Catholic ethics are dependent, to some extent at least, on accepting magisterial authority and teaching. However, it isn't true to say that natural reason can't do something on its own. Well, what is that something?
The 'New Atheist rationalism' assumes that philosophical arguments are short and sweet: if an argument isn't short and sweet and definitely conclusive, it's a sign of irrationality. But a moment's thought indicates that, so far as the humanities are concerned, there are precious few short and sweet arguments. So, for example, it simply isn't true that consequentialism (of any sort) is universally (or even predominantly) accepted by (even non-religious) philosophers as the obviously correct way of doing ethics.* Those familiar with the debates (try here) realize that, whatever their own views, there is nothing of a consensus on this. So, absent revelation, ethics (and other aspects of philosophy) tend to result in long, difficult discussions without any apparent conclusion. That doesn't make them useless. As Rosalind Hursthouse puts it in explaining why she became a vegetarian:
...rational argument has an important part to play, and is sometimes decisive in changing people's minds -but sometimes what is needed to bring about change is rational argument aided by a shift of moral vision.
This is what happened to me....I was not converted to vegetarianism by Singer's and Regan's arguments, but by reading someone else [Stephen R. L. Clark]....Reading his characterizations of the attitudes embodied in what was, at the time, my own view, and, over quite a long period, absorbing them, gradually changed the way I saw things, in particular, my own actions. I began to see those that related to my conception of flesh-foods as unnecessary, greedy, self-indulgent, childish, my attitude to shopping and cooking in order to produce lavish dinner parties as parochial, gross, even dissolute....Without thinking that animals had rights, I began to see both the wild ones and the ones we usually eat, as having lives of their own, which they should be left to enjoy. And so I changed. My perception of the moral landscape and where I and the other animals were situated in it shifted. [Here.]
That sort of shifting in perspective, slow, gradual in build up, but sometimes sudden in that final shift from seeing something one way to seeing it in another, is part of what can sometimes be achieved by rational argument. To do that requires the sort of personal purification that Platonism emphasizes: to be open to a change in view requires a certain sort of character, one that smugness, impatience and pride can prevent.
I confess I find it sometimes difficult to walk away from what is obviously an impossible debate. Partly, it is hope: just one more turn around the block and then you'll have made your point irresistibly and your opponent will cave in. (And, of course, rarely, that does happen which makes it all the more enticing a prospect.) And honesty compels a certain suspicion of humiliation: it is almost certain that you could have argued better -or, even more worryingly, that someone else could have argued better- and you want to make up for that and get it just right.
Reason without revelation is not useless, but it is incomplete. Equally, revelation without a world in which it is revealed and which provides a context for it, is incomplete. A realistic acknowledgement of the limitations of rational discussion, particularly in the diminished form of the combox, shouldn't lead to the conclusion that it is useless. If someone says it's a duck enough times, eventually, it's possible that you'll be able to see it. (But not of course eat it.)
* The statistics from the PhilPapers survey of professional philosophers are:
Normative ethics: deontology, consequentialism, or virtue ethics?
Other 301 / 931 (32.3%)
Accept or lean toward: deontology 241 / 931 (25.9%)
Accept or lean toward: consequentialism 220 / 931 (23.6%)
Accept or lean toward: virtue ethics 169 / 931 (18.2%)