Science is the technique by which we arrive at knowledge of natural phenomena, using the methods of observation, experimentation, replication of experiments, and verification.
Scientism, on the other hand, is the theory, or the belief, that the methods of scientific investigation should be applied to all fields of inquiry. This is something quite different from science, for science often finds itself facing questions which experimental method cannot answer. When confronted with such phenomena, the scientist, understanding the limits of science, normally says nothing. If we cannot subject it to experiment, the phenomenon under question cannot be studied scientifically, and the scientist has nothing to say.
But this doesn't mean that these phenomena can't be studied. I can study my own tastes in art, or your tastes in literature, or his or her tastes in music, without once attempting an experiment, yet still come up with meaningful statements. It is simply the case that many subjects of study require other than scientific methodologies.
But scientism denies this. The belief that scientific methodology should be applied to all fields of study assumes that all phenomena are ultimately reconcilable to experiment. This implies the underlying belief that all phenomena throughout the universe are of the kind that can be rendered in rational terms. This implies the further belief that the universe is ultimately rational, which assumes that all phenomena can be accurately described by using words and numbers. But in order to convey meaning with words, we must organize them into linear 'strings', and this leads us to the assumption that all phenomena can be likewise organized into strictly linear patterns. These are all huge assumptions, all reflected bias, none with solid grounds.
Scientism is not science. Scientism is a pseudo-scientific belief, which is based partly upon a naive understanding of what science is and what it can do. It is also based upon a naïve understanding of the world around us, and naive assumptions about how we come to understand this world.
Science must accept and deal with the fact that certain of its assumptions are unprovable, and must always be so. The so-called 'problem of induction' has never been solved, and probably never will be. Induction is the means by which we reason from particular instances to general principles. We observe many particular instances of the sun rising in the east. We reason from these particular instances that a general principle - 'The sun rises in the east' - is valid. The problem here arises in the fact that induction by itself gives us no guarantee that further particular instances will occur. The fact that we have all seen the sun rising in the east every morning of our lives does not, by itself, guarantee that the sun will do the same thing tomorrow. Induction makes us no such promises. All the arguments we may bring forward to support our belief that the sun will rise tomorrow are themselves based upon induction, which compounds the problem. When we have done with all the arguing, we are left right where we were at the beginning, without certainty.
Yet all of science is based upon the validity of induction. We do not perceive general principles. We perceive particular instances. It is by observing these particular instances under controlled, experimental conditions, by verifying these observations independently, and so on, that we arrive at that state of knowledge called 'scientific'.
Though unprovable, inductive reasoning has given us great knowledge, and the scientist simply remarks 'it works' and leaves it alone. And it does work. But it cannot be proven. It does not give us certainty. Induction only gives us probability. And this is all science needs.
Scientism is not something all scientists do. In fact, it appears to be something very few practicing members of science do (as opposed to academic science, if that is not an oxymoron). I find that the majority of scientists workng in the field have sufficient daily experience with the ambiguous and the unprovable that they have learned a practical (if not a real) humility. The questions I pepper my scientific colleagues with are almost always met with 'Well, some people think A is the case, others think that B is the case, for myself, I suspect that B or C might be the case, but we'll have to wait to see what further experimentation tells us.' (They never give me certain answers, only probables.)
If I were called upon to name the one characteristic that separates the scientists of the late 20th century from his or her 19th century colleagues, it is in the more sophisticated understanding of ambiguity, and a greater tolerance for open and unsolvable questions. Yet this tolerance for ambiguity appears to be the one characteristic lackng in scientism.
I cannot think of any scientist of my acquaintance who would insist that all fields of study ought to be conducted as science. Yet, apparently, there are still those who believe as H.G. Wells once did, that Ethics and the like ought to be conducted on an empirical basis. Perhaps the notion is that once we have produced a 'scientific ethic' people will start behaving themselves. Or perhaps the notion is not even that we7al thought out - perhaps the modern promoters of scientism are indeed proposing something as crude as Wells' 'enlightened tyranny of benevolent scientists', on the child-like view that scientists are less effected by the human failings and imperfections that bedevil the rest of us. Hiroshima ought to have disabused us of that by now.
Scientism is possibly a hangover from the pre-relativistic days of Spinoza's clockwork universe. But Spinoza's clockwork universe (which he concocted in an effort to reconcile the apparent paradox between the omnipotence of God and the Free Will of Humanity), provides a not-veryhelpful model of natural phenomena, one which explains little. The clockwork, or mechanistic universe was a drearily predictable place, one which made the claim that every event could be organized and catalogued into a single all-encompassing system. Relativity put an end to that. (it is interesting to note, in this context, the primary metaphysical motives that were the foundation of much of 19th century, pre-relativistic science.)
Scientism itself is an anti-scientific, anti-rational belief. We have nothing, except wishful thinking, perhaps, to support the belief that all fields of study require, or would even be improved, by scientific method. This belief is a naive tribute to the efficacy of science. Science produces results, astonishing results. Ethics does not. People still lie, steal, cheat, rape and maim today just as they have for the past ten thousand years. Perhaps (I suspect the reasoning goes) if we start studying Ethics the way we study science, we will start producing the same astonishing results, and someday live in a world without war. Many times, all we need do is state a belief in order to make the fallacies clear, and the previous statement is an example of that. Ethics is a type of study different than science, and its results cannot be measured. The fact that crimes are committed today, as they have been for thousands of years, does not indicate a 'lack of progress' or- that the study of Ethics must be improved. It is not the goal of Ethics to produce the quantitative results that science does.
Ethics seeks qualitative results, and in the study of qualities, science has nothing to offer. The qualitative studies - art, literature, poetry, dance, music, in some cases philosophy - work with entirely different principles, different goals. Where science seeks generalized truths, and has little use for the eccentric, the qualitative studies are based upon eccentric phenomena, the personality of individuals, the quirks of time and fashion, the irreproducible results of paint splatter and wordplay.
Thus, scientism excludes, ignores, or has no comprehension of, whole areas of study which have given us immeasurable knowledge. Yet I have occasionally run across these promoters of 'scientism', and usually among the academic studies, science educators and the like.
If it is indeed the case that scientism is strictly an academic bias, one which has no circulation outside academia, then we need not concern ourselves with it, for aside from confusing a few students (which is a good exercise for them - nothing like a bit of confusion to teach you how to think for yourself is it a moribund belief, one which cannot survive except in the artificial world of books.