In the course of an essay offering a modest defense of Martin Heidegger in advance of the publication of Heidegger’s Black Notebooks, a collection of private reflections that, among other things, demonstrate the philosopher’s deeply anti-semitic views, Jonathan Rée gives his definition of philosophy:
The point about philosophy is not that it offers an anthology of opinions congenial to us, which we can dip into to find illustrations of what you might call greeting card sentiments. Philosophy is about learning to be aware of problems in your own thinking where you might not have suspected them. It offers its readers an intellectual boot camp, where every sentence is a challenge, to be negotiated with care. The greatest philosophers may well be wrong: the point of recognising them as great is not to subordinate yourself to them, but to challenge yourself to work out exactly where they go wrong.
Not a bad view of philosophy.