The conclusion summarizes some of the main theses of the book. In the past century, the view that philosophy aims at knowledge and methods to acquire knowledge has been abandoned, and this has contributed to the increasing irrelevance of the subject. The book attempts to revive this view. This requires a rethinking of knowledge. According to it, knowledge is a natural process, continuous with the biological process by which life is sustained and evolved. Specifically, knowledge is problem solving by the analytic method, so it does not consist of truths but of plausible hypotheses, and is never definitive, hence it is an ongoing process. That knowledge is problem solving by the analytic method applies to all kinds of knowledge, from perceptual knowledge to scientific and mathematical knowledge. The importance of a rethinking of knowledge depends on the fact that knowledge plays a central role in human life at all levels, from survival to improving the quality of life, and is also a precondition of happiness.