The dramatic and ongoing changes in the funding of science have stimulated interest in an economics of scientific knowledge (ESK), which would investigate the effects of these changes on the scientific enterprise. Hands (1994) has previously explored the lessons for such an ESK from the existing precedent of the sociology of scientific knowledge (SSK). In particular, he examines the philosophical problems of SSK and those that any ESK in its image would face. This paper explores this argument further by contending that more recent literature in SSK exposes even deeper philosophical problems than those identified by Hands. Meaning finitism has emerged as the philosophical core of SSK. An examination of the profound problems with this position is used to show that an underlying extensionalism is the root of SSK’s intractable philosophical difficulties, and to illustrate the entirely different approach of a critical philosophy that is advocated in its place. In this way, the project of an ESK is shown to depend upon a critical philosophy.