I find myself in the position that Jerome Bruner (1976) found himself in a few years before me. I agreed to give a Herbert Spencer lecture; I planned to give a lecture on the topic of scientific explanation; I intended to discuss a particular controversy in that field, the controversy about whether scientific theories are ‘incommensurable’, about whether there is any ‘convergence’ in scientific knowledge; but I felt increasing dissatisfaction with this entire idea as the day approached. Bruner's dissatisfaction led him to some reflections about the history and present state of psychology. I intend to follow his example and ruminate on the activity itself, the activity of philosophy of science, in my own case, and on certain dissatisfactions I feel with the way that activity has been pursued, rather than discuss a particular issue within it. However, the particular issue I mentioned will come up in the course of these ruminations.

Logical positivism is self-refuting

In the late 1920s, about 1928, the Vienna Circle announced the first of what were to be a series of formulations of an empiricist meaning criterion: the meaning of a sentence is its method of verification. A. J. Ayer's Language, Truth and Logic spread the new message to the English-speaking philosophical world: untestable statements are cognitively meaningless. A statement must either be (a) analytic (logically true, or logically false to be more precise) or (b) empirically testable, or (c) nonsense, i.e., not a real statement at all, but only a pseudostatement. Notice that this was already a change from the first formulation.