One of my colleagues set me to reading papers in the psychology of perception, particularly the Gestalt psychologists; another introduced me to B. L. Whorf’s speculations about the effect of language on world view; and W. V. O. Quine opened for me the philosophical puzzles of the analytic-synthetic distinction. That is the sort of random exploration that the Society of Fellows permits, and only through it could I have encountered Ludwik Fleck’s almost unknown monograph, Entstehung und Entwicklung einer wissenschaftlichen Tatsache (Basel, 1935), an essay that anticipates many of my own ideas.