Developing the view that philosophy is acquisition of knowledge requires answering several questions about knowledge. The first question, of course, is: What is knowledge? A widely held view is that this question is a demand to give an analysis of the concept of knowledge. But this conflict with the fact that every analysis of the concept of knowledge is subject to counterexamples. Alternatively, the chapter argues that the question ‘What is knowledge?’ is a demand to give an analysis of the function of knowledge in human life, and in general in the life of all organisms. And the answer to this demand is that knowledge is a life function that serves to solve problems of biological life and, in the case of human beings, also problems of cultural life.