Apologists for theism often point out, correctly, that science cannot tell us why things happen, but only what happens and how. As what was once called natural history, what we have lately called science can provide, not explanations, strictly speaking, but rather only more or less precise and accurate descriptions (and their formalizations). Proper scientists would as natural historians presumably be the first to agree. Scientism, the metaphysical doctrine erected upon this lacuna of science, argues that it is due to there being no such thing in reality as a why; no purpose, no end or telos or reason to things. Devotees of scientism rarely notice that if there is no reason to things, there is then no possibility of explaining or understanding them; so that scientism, if true, is incomprehensible.
The devotees of scientism render themselves absurd, and we needn’t trouble ourselves further with their arguments against competing metaphysical theories.
This of course does not at all mean that we may disregard science or its findings; nor does it mean that there is any necessary correlation between being a scientist, or as a scientific layman crediting the discoveries of science, and being an absurd devotee of scientism. It is perfectly possible, in other words, to be a believer in science, its findings and methods, and to be rational and coherent.
But this is possible only for those who are ready to admit that there must be a purpose, a reason and therefore an explanation of things, even though science cannot tell us what it might be. Indeed, it is possible only for those who are ready to admit that science cannot even get started unless there be such reasons and purposes.
This because the what and how of a thing – which are subsumed under the venerable term “quiddity” (after the Latin quid, “what, how[?]“) – are not intelligible except under a presupposition of their reasonableness – their sufficient reason, their purpose, telos, final end, &c. - which we might subsume under the neologism “currity” (after the Latin cur, “why, wherefore[?]“). Strictly speaking, we cannot give an adequate account of what a thing is, or how it works (the latter being an aspect of the former), without an account of why it does what it does and is what it is.
An account of how a thing works is part of any complete account of that thing’s quiddity. But the working of a thing is not fully intelligible without reference to its characteristic effects or products, its results or sequelae. Implicit in any connection we draw between such sequelae of a thing and the thing itself is the question, “what makes this thing do what it does?” Or, i.e., “why does this thing do what it does?” Indeed, the answer to this question just is the connection we draw between a thing and its sequelae. Without such an answer, there is no connection. And without that whole congeries of reasonable connections between things, there can be no such thing as a causal order, properly so-called; and, thus, no proper object of science, or objective of scientific work.
If science is to get started at all, then, it must presuppose the objective reality of such a network of reasonable connections between things. It must presuppose there is such a thing as a science of teleology.