The Mirror of Philosophers, and Science: A.J. Ayer speaks about philosophers’ common qualities, in relation to the sciences. From the interview:

“Wittgenstein was interested in fundamental philosophical problems, Austin in language for its own sake,” Ayers said. Yet Austin, despite Gellner, was not a linguist, in any ordinary sense of the word; he was interested in etymology or in the growth of language. He applied himself only to the function of words.” He agreed that there was some truth in the view that philosophy for Austin was an impersonal investigation but for Wittgenstein was intensely personal. Indeed, Wittgenstein thought of himself as a living philosophical problem….

I racked my sleepy brain for some more questions, and finally asked him whether there was one particular quality that all philosophers shared.

He was thoughtful for a moment and then said, “Vanity. Yes, vanity is the sine qua non of philosophers. In the sciences, you see, there are established criteria of truth and falsehood. In philosophy, except where questions of formal logic are involved, there are none, and so the practitioners are extremely reluctant to admit error. To come back to Austin, no one would deny the incisive quality of his mind, and yet when Strawson defeated him in an argument about Truth, it never seemed to have once crossed Austin’s mind that he was the vanquished. To take another example, Russell attacks Strawson as if he were just another Oxford philosopher, without reading him carefully. But perhaps at his age Russell has a right to make up his mind about a book without reading it.” Some of the philosophers were vain not only about their thoughts but also about their personal influence, Ayer added. Wittgenstein dominated his classes, and, of course, Austin was an absolute dictator at his Saturday mornings.

Ved Mehta, The Fly and the Fly-Bottle