Originally published in 1963. Can one discern certain regularities in the manoeuvrings and techniques employed by scientists and can these be formulated into the methodological principles of science? What is the origin and basis of such principles? Are they imposed by objective realities, do they derive from conceptual necessities or are they rooted in our own deep seated predilections? This volume investigates these questions and sheds light on the growth mechanism of the evolving structure of science itself.