Somehow, the practice of astronomy, physics, chemistry or biology normally fails to evoke the controversies over fundamentals that today seem endemic among, say, psychologists or sociologists. Attempting to discover the source of that difference led me to recognize the role in scientific research of what I have since called paradigms. These I take to be universally recognized scientific achievements that for a time provide model problems and solutions for a community of practitioners.

p. 48. - The Structure of Scientific Revolutions (1962)