The driving question is: How can we know what the world is really like? At core, philosophy is about metaphysics. If philosophers (and most people) study anything, they study how the world really is! From our simplest questions of how many chairs there are in a room to the nature of justice and right and wrong, we are asking the same question: How is the world, really?
That question down through history has been addressed in two broad strands: rationalism and empiricism.
Plato was a rationalist. Aristotle was an empiricist. And from those early beginnings, the debate has raged down to the time of Descartes and Hume, who were both the paradigm representatives of rationalism and empiricism respectively.
A rationalist points to the undisputed fact that empiricism is unreliable (being contingent and relative) and says, “Look, if you really want to know how the world really is, really, truly, then you cannot rely on the senses. The senses are dead-on-arrival if you care about knowing reality. The senses deceive you all the time, so they cannot in principle be the basis for reliable knowledge of the world. Thus, we must appeal to pure reason alone to discover the truths of the world.”
The empiricist responds, “Sure, the senses are unreliable, but if enough people put their reports together, we can get a very accurate and ‘reliable-enough’ picture of the world from all of those reports. And your rationalist idea that it is possible to get a ‘perfectly reliable’ picture of the world just from reason alone is absurd! Reason alone can only tell you about general forms and abstractions. It cannot tell you anything substantive about the world. It is like formal logic with no content in the form. So, at best, you are talking about abstractions rather than reality!”
The empiricist charge that rationalists are not saying anything substantive about the world is serious indeed! After all, there is nothing truly metaphysical going on in the claim: “Bachelors are unmarried males.” Such a claim is merely, as Hume said, “relations of ideas,” which are empty of actual content.
By contrast, it is also serious indeed when the rationalists charge that empiricists are relying upon unreliable evidence about appearances only, so empiricists are not actually touching the “real world” at all. Thus, empiricist “metaphysics” are really falsely-so-called!
The goal is reliable metaphysics that is also making substantive discoveries about the actual, real world.
Both rationalism and empiricism have foundered in their efforts to do effective metaphysics.
Science’s response to this foundering is: “Silly philosophers! What a worthless bunch of babbling. You keep talking round and round and getting nowhere. Meanwhile, we will just keep producing an endless string of successes, which demonstrates pretty compellingly that metaphysics is really just physics. So, you keep your silly ‘metaphysics,’ while we produce substantive claims about how the world really does work, and we’ll have the working evidences to prove it.”
And there things stand. Rationalism is all but dead. Empiricism has become synonymous with science. And science claims that it is doing the only real and effective metaphysics that has ever been done in human history. Revelation is laughed at, called “blind faith without reason or evidence.” And the power and intellectual prestige of the scientific community only grows and grows.
The enlightenment seems synonymous with empirical metaphysics grounded in the scientific method. “Reason” just means scientific inquiry. And God is non-existent or absent.
Well…. not so fast. The rationalism/empiricism divide is not all there is to metaphysics. And the enlightenment was far more than merely a scientific revolution.