Any account of knowledge has to take account both of the contribution of the world and the contribution of man. Every human endeavour, every activity, every art, every science is a product of a unique interaction between man and the world. Where man is most passive, he merely reflects and reports the world; this is pure discovery, if it ever exists. Where man is most active, the world's contribution lies merely in the provision of the raw material; this is pure invention, if it ever exists. All the arts, all the sciences can be ordered in a continuous array or spectrum ranging from pure discovery to pure invention. That they are all at some point on this continuum gives them a common but fragile thread, justifying our thinking and talking of the unity of the arts and sciences. Philosophy is neither pure discovery nor pure invention; it bears resemblances to both a science and an art. In this paper I propose to try to give reasons why we should regard the philosopher as an artist and philosophy as an art; or, at any rate, I shall try to show that there is an Art of Philosophy.