Bloor's (1991) defense of a naturalized study of knowledge implies the search for a general causal theory about cognitive phenomena. Such a theory has to explain all cognitive beliefs; that is, all of them have to appear as part of the same causal process, and all have to be the effect of the same kinds of causes. But, Bloor says, the problem with this demand is that the set of cognitive beliefs has been divided, traditionally, into a positive and a negative side, namely, the correct, true, rational beliefs, on the one hand, and the incorrect, false, irrational beliefs on the other. Moreover, and here is the point, for each of these sides one has a different kind of explanation. While the beliefs on the positive side members of an autonomous intellectual realm are explained by the exclusive action of internal factors, typically scientific rules and facts, those on the negative side are explained, instead, by referring to external factors typically psychological and sociological.27 In this way, differences in the set of beliefs give way to the dichotomization of their causes, and this turns out to be an obstacle to the construction of a single causal explanatory theory of knowledge. Bloor's principle of symmetry intends, precisely, to block this dichotomization: if social factors have causal efficacy, they have it for all beliefs alike. That is, the field of sociological investigation should not be limited to the pathology of beliefs. This is indeed the way Bloor introduces and presents arguments for his principle. The possibility of a positive answer to Bloor's question about the propriety of sociological incursion into epistemological matters is, thus, blocked by this radical distinction between internal and external factors and their causal efficacy. The rejection of this distinction is, indeed, the negative content of the principle of symmetry, whose positive side would be the demanding of a role for sociology in science studies.

One could say that to read the symmetry principle in this way is to give it a weak interpretation even weaker than Bloor himself wanted. Indeed, the meaning of "strong" as in Strong Program has been understood as having to do with a reductionist oversociologization of knowledge's explanation; namely, in knowledge causation social factors would have priority if not exclusivity. There would be no causal role for reality to play. But this last reading cannot be supported because of what the very text that introduces the principle really says. AndBloor<>

This misunderstanding about the use of the term "strong" could be a reason for the persistent rejection of a demand for a role for sociology in science studies. This rejection continues today, in spite of the fact that sociology's integration could appear as a further step in the transformation of philosophy which gave rise to its naturalization. In effect, philosophy was the first of the science studies in this century as a normative foundationalist discipline. This meant, at the time, that there had to be a sharp demarcation between the task of philosophers, on the one hand, and that of historians, pscychologists, and sociologists, on the other. The first transformation came as a consequence of Kuhn's demand for a role for history and Lakatos's proposal to deal with a metascientific investigation program as if it were an historiographical one. With this change, the normative versus descriptive distinction became the internal versus external distinction. And this in turn meant, as I have said, that Lakatos opened the door to history with the same firmness that he closed it to psychology and sociology. The later transformation occurs with the naturalization of epistemology: the demand which originates with Quine although it has a very different meaning today to deal with knowledge as a natural phenomenon. This opens the door to science studies to psychology and, almost simultaneously, to biology. Science studies became, thus, truly interdisciplinary. But the traditional thesis about the autonomy of science the core of the internalist view continues to block the possibility of "a naturalist understanding of knowledge in which sociology plays a role."