By Thomas S. Kuhn ^*

At the University of Chicago, the façade of the Social Science Research
Building bears Lord Kelvin's famous dictum: "If you cannot measure,
your knowledge is meager and unsatisfactory." ¹ Would that statement be there
if it had been written, not by a physicist, but by a sociologist, political scientist,
or economist? Or again, would terms like "meter reading" and "yardstick"
recur so frequently in contemporary discussions of epistemology and scientific
method were it not for the prestige of modern physical science and the fact
that measurement so obviously bulks large in its research? Suspecting that
the answer to both these questions is no, I find my assigned role in this con-
ference particularly challenging. Because physical science is so often seen as
the paradigm of sound knowledge and because quantitative techniques seem
to provide an essential clue to its success, the question how measurement has
actually functioned for the past three centuries in physical science arouses
more than its natural and intrinsic interest. Let me therefore make my gen-
eral position clear at the start. Both as an ex-physicist and as an historian of
physical science I feel sure that, for at least a century and a half, quantitative
methods have indeed been central to the development of the fields I study.
On the other hand, I feel equally convinced that our most prevalent notions
both about the function of measurement and about the source of its special
efficacy are derived largely from myth.

Partly because of this conviction and partly for more autobiographical rea-
sons, ² I shall employ in this paper an approach rather different from that of
most other contributors to this conference. Until almost its close my essay
will include no narrative of the increasing deployment of quantitative tech-
niques in physical science since the close of the Middle Ages. Instead, the two

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