Mary Midgley in The Owl of Minerva: A Memoir, Routledge, 2005, p. 13, reminisces about her headmistress, Miss Annie Bowden:
I also remember something striking that she had said when I had complained that I knew the answer to some question but I just couldn't say it clearly. 'If you can't say a thing clearly,' she replied, 'then you don't actually know what it is, do you?' This is a deep thought which I have often come back to, and it is in general a useful one. It lies at the heart of British empiricism. Though it is not by any means always true, I am glad to have had it put before me so early in life. It's a good thought to have when you are trying to clarify your own ideas, but a bad one when you are supposed to be understanding other people's. Philosophers are always complaining that other people's remarks are not clear when what they mean is that they are unwelcome. So they often cultivate the art of not understanding things -- something which British analytic philosophers are particularly good at. (Bolding added.)
My added emphasis signals my approbation.
We owe it to ourselves and our readers to be as clear as we can. But the whole point of philosophy is to extend clarity beyond the 'clarity' of everyday life and everyday thinking. The pursuit of this higher clarity, the attempt to work our way out of Plato's Cave, results in a kind of talking and thinking that must appear obscure to the Cave dweller. Well, so much the worse for him and his values. To demand Cave clarity of the philosopher is vulgar and philistine. Got that, Ludwig?
For more on this topic, see Adorno on Wittgenstein's Indescribable Vulgarity.