The Enlightenment has been widely described as an age of reason, but the moderate Enlightenment — at least until Kant — put many more limits on reason, especially in areas like religion and politics, than Plato and Aristotle did.
Kant made the autonomy of reason — its non-subordination to anything else — an explicit theme. Rhetorically, of course, he also famously talks about limits on reason, but really what he wants to limit are extra-rational accretions woven into Cartesian and Wolffian rationalisms — various received truths, and so on. Descartes had quickly moved from hyperbolic doubt to question-begging acceptance of many received truths as intuitively reasonable. Wolff and his followers, to whom Kant was primarily reacting, did not even pretend to doubt.
If reason is to be truly autonomous, it cannot start from received truths. Kant himself was sympathetic to some of these received truths, but too honest to pretend they were self-evident or derivable from reason alone. Kant is often misunderstood as mainly a critic of reason, and certainly not its unconditional defender, but he is actually clear that the autonomy of reason is unconditional. Too often, readers of Kant focus too much on autonomy of a subject rather than autonomy of reason, but the practical autonomy attributable to a so-called subject in Kant is actually derivative, based on the putative subject’s participation in the autonomy of reason. In Making It Explicit, Brandom says where Descartes had focused on our grip on concepts, Kant focused instead on their grip on us (p. 9). (See also Kant’s Groundwork.)
Hegel has been widely misunderstood as an example of the autonomy of reason gone mad. Brandom, Pippin, and Pinkard have performed an invaluable service in clarifying what Hegel was really trying to do, which was in part to sincerely take up Kant’s honesty about received truths and to push it even further.
Aristotle said that of all things, reason most deserves to be called divine. He does not use a word like autonomy, but the effect is the same. Nothing is higher. (See also Interpretation; Brandom on Truth.)
I think of the Kantian autonomy of reason as necessarily involving something like the free play of the Critique of Judgment.