Jerry Fodor's "Is Science Biologically Possible?" (in Beilby, ed. Naturalism Defeated? Cornell UP 2002, pp. 30-42) begins like this:
I hold to a philosophical view that, for want of a better term, I'll call by one that is usually taken to be pejorative: Scientism. Scientism claims, on the one hand, that the goals of scientific inquiry include the discovery of objective empirical truths; and, on the other hand, that science has come pretty close to achieving this goal at least from time to time. The molecular theory of gasses is, I suppose, a plausible example of achieving it in physics; so is the cell theory in biology; the theory, in geology, that the earth is very old; and the theory, in astronomy,that the stars are very far away . . . .
I'm inclined to think that Scientism, so construed, is not just true but obviously and certainly true; it's something that nobody in the late twentieth century who has a claim to an adequate education and a minimum of common sense should doubt.
Up to this point one might get the impression that Fodor is simply stipulating that he will use 'scientism' in his own perverse and idiosyncratic way. But then he goes on to say that scientism is under attack from the left and from the right: "on the left, from a spectrum of relativists and pragmatists, and on the right, from a spectrum of Idealists and a priorists."
At this point I threw down the article in disgust and went on to something worthwhile.
If you want to take a term in widespread use, a term the meaning of which is more or less agreed upon by hundreds of philosophers, and use it in our own crazy-headed way, that, perhaps, may be forgiven. But it is utterly unforgivable to use one and same term with both the received meaning and your crazy-headed arbitrarily stipulated meaning.
What is scientism? I expect some bickering over the particulars of the following definition, but I believe the following captures in at least broad outline what most competent practioners understand by 'scientism.'
Scientism is a philosophical thesis that belongs to the sub-discipline of epistemology. It is not a thesis in science, but a thesis about science. The thesis in its strongest form is that the only genuine knowledge is scientific knowledge, the knowledge generated by the (hard) sciences of physics, chemistry, biology and their offshoots. The thesis in a weaker form allows some cognitive value to the social sciences, the humanities, and other subjects, but insists that scientific knowledge is vastly superior and authoritative and is as it were the 'gold standard' when it comes to knowledge. On either strong or weak scientism, there is no room for first philosophy, according to which philosophy is an autonomous discipline, independent of natural science, and authoritative in respect to it. So on scientism, natural science sets the standard in matters epistemic, and philosophy’s role is at best ancillary. Not a handmaiden to theology in this day and age; a handmaiden to science.
One problem with strong scientism is that it is self-vitiating, as the following argument demonstrates:
a. The philosophical thesis of strong scientism is not an item of scientific knowledge.
b. All genuine knowledge is scientific knowledge.
c. The philosophical thesis of strong scientism is not an item of genuine knowledge.
Hence one cannot claim to know that scientism is true if it is true. Scientism falls short of the very standard it enshrines. It is at most an optional philosophical belief unsupported by science. It also has unpalatable consequences which for many of us have the force of counterexamples.
If scientism is true, then none of the following can count as items of knowledge: That torturing children for fun is morally wrong; that setting afire a sleeping bum is morally worse than picking his pockets; that raping a woman is morally worse than merely threatening to rape her; that verbally threatening to commit rape is morally worse than entertaining (with pleasure) the thought of committing rape; that 'ought' implies 'can'; that moral goodness is a higher value than physical strength; that might does not make right; that the punishment must fit the crime; that a proposition and its negation cannot both be true; that what is past was once present; that if A remembers B's experience, then A = B; and so on. In sum: if there are any purely rational insights into aesthetic, moral, logical, or metaphysical states of affairs, then scientism is false. For the knowledge I get when I see (with the eye of the mind) that the punishment must fit the crime is not an item of scientific knowledge.
Back to Fodor. His definition of scientism has nothing to so with scientism as commonly understood. The latter is a highly dubious philosophical thesis as I have just demonstrated. But what he calls scientism is but a platitude that most of us will accept while rejectiong scientism as commonly understood.