The development from Aquinas through Locke and Newton represents more than four hundred years of stumbling, tortuous, prodigious effort to secularize the Western mind, i.e., to liberate man from the medieval shackles. It was the buildup toward a climax: the eighteenth century, the Age of Enlightenment. For the first time in modern history, an authentic respect for reason became the mark of an entire culture; the trend that had been implicit in the centuries-long crusade of a handful of innovators now swept the West explicitly, reaching and inspiring educated men in every field. Reason, for so long the wave of the future, had become the animating force of the present.
Confidence in the power of man replaced dependence on the grace of God — and that rare intellectual orientation emerged, the key to the Enlightenment approach in every branch of philosophy: secularism without skepticism.
In metaphysics, this meant a fundamental change in emphasis: from God to this world, the world of particulars in which men live, the realm of nature . . . . Men’s operative conviction was that nature is an autonomous realm — solid, eternal, real in its own right. For centuries, nature had been regarded as a realm of miracles manipulated by a personal deity, a realm whose significance lay in the clues it offered to the purposes of its author. Now the operative conviction was that nature is a realm governed by scientific laws, which permit no miracles and which are intelligible without reference to the supernatural.
Just as there are no limits to man’s knowledge, many [Enlightenment era] thinkers held, so there are no limits to man’s moral improvement. If man is not yet perfect, they held, he is at least perfectible. Just as there are objective, natural laws in science, so there are objective, natural laws in ethics; and man is capable of discovering such laws and of acting in accordance with them. He is capable not only of developing his intellect, but also of living by its guidance. (This, at least, was the Enlightenment’s ethical program and promise.)
Whatever the vacillations or doubts of particular thinkers, the dominant trend represented a new vision and estimate of man: man as a self-sufficient, rational being and, therefore, as basically good, as potentially noble, as a value.
The father of this new world was a single philosopher: Aristotle. On countless issues, Aristotle’s views differ from those of the Enlightenment. But, in terms of broad fundamentals, the philosophy of Aristotle is the philosophy of the Enlightenment.
In epistemology, the European champions of the intellect had been unable to formulate a tenable view of the nature of reason or, therefore, to validate their proclaimed confidence in its power. As a result, from the beginning of the eighteenth century (and even earlier), the philosophy advocating reason was in the process of gradual, but accelerating, disintegration.