Clinical decisionmaking includes reasoning from prescientific or scientific theories, reasoning from uncontrolled or controlled experience, and reasoning based on empathic understanding and moral beliefe. The development of contemporary clinical thinking is discussed, and it is found that successive generations of medical practitioners have had different views of the rationality and relative importance of these modes of reasoning: that which is considered rational by one generation of doctors is sometimes denounced by the next. The author's book, Rational Diagnosis and Treatment, which is an example of clinical thinking in the 1960s and early 70s, is used to illustrate one particular view of clinical decisionmaking.