Scientism is defined by the Merriam-Webster dictionary as:
1: methods and attitudes typical of or attributed to the natural scientist
2: an exaggerated trust in the efficacy of the methods of natural science applied to all areas of investigation (as in philosophy, the social sciences, and the humanities)
The term “scientism” is anything but clear, more of a boo-word than a label for any coherent doctrine. Sometimes it is equated with lunatic positions, such as that “science is all that matters” or that “scientists should be entrusted to solve all problems.” Sometimes it is clarified with adjectives like “simplistic,” “naïve,” and “vulgar.” The definitional vacuum allows me to replicate gay activists’ flaunting of “queer” and appropriate the pejorative for a position I am prepared to defend.
Scientism, in this good sense, is not the belief that members of the occupational guild called “science” are particularly wise or noble. On the contrary, the defining practices of science, including open debate, peer review, and double-blind methods, are explicitly designed to circumvent the errors and sins to which scientists, being human, are vulnerable. Scientism does not mean that all current scientific hypotheses are true; most new ones are not, since the cycle of conjecture and refutation is the lifeblood of science. It is not an imperialistic drive to occupy the humanities; the promise of science is to enrich and diversify the intellectual tools of humanistic scholarship, not to obliterate them. And it is not the dogma that physical stuff is the only thing that exists. Scientists themselves are immersed in the ethereal medium of information, including the truths of mathematics, the logic of their theories, and the values that guide their enterprise. In this conception, science is of a piece with philosophy, reason, and Enlightenment humanism. It is distinguished by an explicit commitment to two ideals, and it is these that scientism seeks to export to the rest of intellectual life.
The first is that the world is intelligible. The phenomena we experience may be explained by principles that are more general than the phenomena themselves. These principles may in turn be explained by more fundamental principles, and so on. In making sense of our world, there should be few occasions in which we are forced to concede “It just is” or “It’s magic” or “Because I said so.” The commitment to intelligibility is not a matter of brute faith, but gradually validates itself as more and more of the world becomes explicable in scientific terms. The processes of life, for example, used to be attributed to a mysterious élan vital; now we know they are powered by chemical and physical reactions among complex molecules.
The second ideal is that the acquisition of knowledge is hard. The world does not go out of its way to reveal its workings, and even if it did, our minds are prone to illusions, fallacies, and superstitions. Most of the traditional causes of belief—faith, revelation, dogma, authority, charisma, conventional wisdom, the invigorating glow of subjective certainty—are generators of error and should be dismissed as sources of knowledge. To understand the world, we must cultivate work-arounds for our cognitive limitations, including skepticism, open debate, formal precision, and empirical tests, often requiring feats of ingenuity. Any movement that calls itself “scientific” but fails to nurture opportunities for the falsification of its own beliefs (most obviously when it murders or imprisons the people who disagree with it) is not a scientific movement.
In a follow-up article he adds:
Science is not a listing of empirical facts, nor has philosophy ever confined itself to the non-empirical.
It is important not to take the definition what science is or how it works for granted. Imre Lakatos lectured about the attitude and consequences of pursuing the problem of demarcation:
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The problem of demarcation between science and pseudoscience has grave implications also for the institutionalization of criticism. Copernicus's theory was banned by the Catholic Church in 1616 because it was said to be pseudoscientific. It was taken off the index in 1820 because by that time the Church deemed that facts had proved it and therefore it became scientific. The Central Committee of the Soviet Communist Party in 1949 declared Mendelian genetics pseudoscientific and had its advocates, like Academician Vavilov, killed in concentration camps; after Vavilov's murder Mendelian genetics was rehabilitated; but the Party's right to decide what is science and publishable and what is pseudoscience and punishable was upheld. The new liberal Establishment of the West also exercises the right to deny freedom of speech to what it regards as pseudoscience, as we have seen in the case of the debate concerning race and intelligence. All these judgments were inevitably based on some sort of demarcation criterion. And this is why the problem of demarcation between science and pseudoscience is not a pseudo-problem of armchair philosophers: it has grave ethical and political implications.