All recent studies on the history and philosophy of science have emphasized that hypotheses and theories always come before observation and always condition what will be observed. The idea that scientists observe in a theoretical vacuum and only then incorporate their observations into a hypothesis or theory has been utterly discredited. All observations are theory-laden, and what is observed will always depend on the hypothesis held by the observer. Paradoxically, those most in thrall to theory are those who deny its importance: They fail to recognize that their own observations are dependent on the theories they hold.
Take one very simple example of which I have just become aware. In the late 18th and early 19th centuries one theory of brain organization held that the convolutions of the cerebral cortex were expressions of individuality and hence could exhibit no consistent pattern from person to person. Otherwise reliable observers carefully studied ...
