Russell is generally credited with being one of the founders of analytic philosophy. He was deeply impressed by Gottfried Leibniz (1646–1716), and wrote on every major area of philosophy except aesthetics. He was particularly prolific in the fields of metaphysics, logic and the philosophy of mathematics, the philosophy of language, ethics and epistemology. When Brand Blanshard asked Russell why he did not write on aesthetics, Russell replied that he did not know anything about it, though he hastened to add "but that is not a very good excuse, for my friends tell me it has not deterred me from writing on other subjects".