William James is widely regarded as America's greatest philosopher. He is also considered to be the father of modern psychology. The Principles of Psychology took him 12 years to write. He considered psychology a natural science that required analysis of feelings, desires, cognitions, reasoning, and decisions according to their own features and dynamics, in the same way that one would explain building a house by looking at its component parts. The Principles of Psychology is one of the few 19th century works on the subject to be cited continuously to this day.