Here’s a capsule history of the transition from medieval Scholasticism to the Enlightenment. Following Aristotle, Scholastics like Thomas Aquinas held that a complete understanding of any natural phenomenon requires attention to each of its four causes. Consider a cat. There is its material cause, which is what it’s made out of—flesh, as opposed to the inorganic matter of which stones and dirt are composed. There is its formal cause, which is its nature or essence—felinity, with all the catlike qualities and behaviors that that entails. There is its efficient cause, which is what brought it into existence—its parents. And there is its final cause, the battery of ends or goals toward which it tends—chasing mice, making other cats, and so on.

Of course, there is more to the story. What exactly distinguishes flesh from other kinds of matter? What exactly is the mechanism by which cats make new cats? These questions too require answers, but finding those answers will entail identifying further causes of each of the four kinds referred to. How do we determine these causes? Through observation, naturally. It is through our experience of cats that we know that they come from other cats, that they tend to seek out mice, and so forth.

Didn’t God play a role? Yes, but not in the crude way New Atheists like Richard Dawkins or Sam Harris would suppose. “God did it” was not the Scholastics’ preferred mode of explanation. Nature’s relationship to God was seen as analogous to a story’s relationship to its author. The story as a whole wouldn’t exist in the first place if there were no author. But to understand the characters, events, and other details of the story, you can just focus on the story itself without constantly asking what the author had in mind. Similarly, though the natural world would not exist without God, you needn’t keep asking yourself what God intended in order to know a thing’s material, formal, efficient, and final causes. You can just study the things themselves.

Medieval thinkers like Aquinas were Big Picture men. They wanted to know the natures of things, and the ends toward which they aim. Hence, formal and final causes got most of their attention. Material and efficient causes, the specific physical mechanisms by means of which a thing realizes the ends set for it by its nature, were of secondary importance. But even the formal and final causes of natural phenomena were ultimately of less interest to the Scholastics than the divine cause of there being any natural world in the first place. Knowing even the most profound details of the story of nature couldn’t compare to knowing its Author.

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The enlightenment shifted these priorities, bringing the Small Picture into focus. Whereas the medievals sought to understand God so as to improve their souls, the Enlightenment was about understanding nature so as to improve our material conditions—to cure diseases, curb natural disasters, harness natural forces, develop new technologies, and so on. Such practical ends required discovery of the specific physical mechanisms by which natural phenomena operate, so that material and efficient causes would now take center stage, and formal and final causes would recede into the background.

In particular, instead of identifying each natural thing’s distinctive essence, Enlightenment science would focus on the way all natural phenomena may be treated as variations on the same basic material stuff—unobservable particles in motion through space. Instead of identifying the distinctive ends or purposes toward which nature aims each thing, the focus would be on identifying the law-like ways in which certain configurations of particles served as the efficient causes of others.

Nature would thus be treated as a machine whose parts and their interactions may be described in an entirely quantitative way. The idea was that, to the extent that the world could be captured by such a mathematical and mechanical model, it could be better predicted and controlled, and the practical aims of the Enlightenment thereby realized. For the Scholastic philosopher, knowledge was about wisdom: understanding and respecting the natures and purposes of things. For fathers of modern science like Francis Bacon and René Descartes, knowledge would be about power: the mastery of nature so as to make it serve our purposes.

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Again, there’s much more to the story than that. But you won’t learn even this much from Harvard psychologist Steven Pinker’s Enlightenment Now. And in the absence of this background, the unwary reader is likely to miss—as Pinker himself does—the book’s fundamental fallacy.

That is not to say that it is a bad book, exactly. In fact, most of it is pretty good. The vast bulk of Enlightenment Now is devoted to demonstrating how astoundingly our material conditions have indeed improved, in every way, in the centuries since the Enlightenment. Life expectancy has increased dramatically. The Green Revolution and genetic engineering have essentially made it possible to eliminate famine. Extreme poverty is disappearing, and in the West a poor person is more likely to be obese than undernourished—and almost always has electricity, running water, a flush toilet, a refrigerator, television, and other amenities which we now take for granted but were unavailable even to the wealthiest persons in previous centuries. The famines and grinding poverty that have occurred in modern times are mostly the results of idiotic socialist economic policy, which we can easily avoid if we want to. Ailments that once killed millions are now treatable, and in some cases have been wiped out entirely. Labor-saving devices have made work far less grueling and increased leisure time. Knowledge has exploded, and can be accessed via the web browser on your cellphone. Death by violence or accident is nowhere near as likely for the average person as it was in past centuries. And so on.

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Pinker, himself a liberal, laments that egalitarians, environmentalists, and other left-wing malcontents are often the most reluctant to want to hear this good news. But page after page of data show not only that these advances are real, but that they are steadily spreading beyond the West to the rest of the world. Nor, in his view, is it deniable that the keys to these advances have been scientific inquiry and its technological bounty, the market economy, and limited government and the rule of law. No Pollyanna, Pinker doesn’t deny that problems remain, but he argues that they are best approached through further application of the methods that have succeeded so well so far. Global warming can be managed by using moderate regulation to harness market forces to control pollution and by expanding nuclear power. Helping the poor must be distinguished from equalizing outcomes, and while the former is a moral imperative, the latter is worse than a distraction and results in policies that only impoverish people further.

The Enlightenment, then, has demonstrably succeeded in improving mankind’s material lot. If only Pinker had left it at that. Unfortunately, he turns his catalog of advances into an apologia for scientism, fallaciously drawing the inference that the methods that have afforded such practical benefits can answer every question, or that if they can’t, then the question must not be worth asking. Though refreshingly nuanced on matters of politics, economics, modern academia, science, and the environment, Pinker is embarrassingly amateurish on questions of philosophy, and turns into a New Atheist hack when addressing religion.

Like the New Atheists, Pinker completely misunderstands the nature of the reasoning that traditional philosophical theology uses to establish the existence of God. He essentially conceives of the deity as a crude “God of the Gaps”—an eccentric cause alongside the others within the universe, posited to account for some specific unusual phenomenon, but who may be dispensed with once a physical cause can be identified. This is like taking the claim that a novel must have an author to mean that there is a certain unusual character alongside the other characters within the story, who does the sorts of things the author is said to do—and then, when a close reading of the novel reveals no such character, taking this as evidence that the author doesn’t exist.

Pinker also shows far less understanding of the grave difficulties facing naturalistic attempts to explain the human mind than do some of the thinkers he admires. He dismisses the Aristotelian idea that there are final causes or purposes built into nature as an “illusion,” the abandonment of which was “perhaps [the] biggest breakthrough” of the scientific revolution. What he fails to see is that this implicitly undermines the very possibility of rationality itself. For it is only if reason has as its natural end or purpose the pursuit of truth that we can say that there is an objective difference between good and bad reasoning. Good reasoning would be reasoning that enables us to attain truth, and bad reasoning would be reasoning that fails to do so. But in a world without final causes, reason cannot aim at truth, because it does not aim at anything at all.

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That is why enlightenment-era philosopher David Hume could famously conclude that reason is “the slave of the passions,” and that there would be nothing contrary to rationality if he were to prefer that the entire world be destroyed rather than he suffer a scratch to his finger. Such a bizarre preference would indeed be as rational as any other if there were no objective fact of the matter about what reason is for. Pinker cites his fellow secular liberal Thomas Nagel in defense of rationality against postmodernism, but seems unaware that even Nagel, professor of philosophy emeritus at New York University, has advocated a reconsideration of Aristotelian final causes precisely as a way to avoid the irrationalist implications of a world in which teleology is absent.

Nor, contrary to what Pinker supposes, can evolution by itself solve the problem. As philosophers of science have often pointed out, even a sophisticated scientific theory that enjoys predictive success and technological application can still turn out to be false. In the same way, an individual person’s set of beliefs can be adaptive and yet be false. Hence, the fact that natural selection has molded our cognitive faculties does not (contra Pinker) entail that those faculties generate true beliefs, but only that they generate adaptive ones.

The common tendency to pit modern science against the medievals’ Aristotelianism thus entails a kind of endarkenment, as it were, of the intellect. Properly understood, the two approaches are complementary rather than in competition. The material advances of the Enlightenment supplement the more other-worldly philosophical and religious wisdom of the ancients and medievals. They do nothing to justify abandoning that wisdom.