We prefer more elegant theories to uglier ones. Why should we think this preference leads to truth?
This is a classic question in the philosophy of science. But I want to raise the question in connection with philosophical theories about fundamental metaphysics, fundamental ethics, philosophy of mathematics and other areas where our interest is necessary rather than contingent truth. Why should we think that the realm of necessity has the kind of aesthetic properties that would make more beautiful theories more likely to be true?
Here are two stories. The first story is that we are so constructed that we tend to find beauty in those philosophical theories that are true. It is difficult to explain why there would be such a coincidence if we are the product of naturalistic evolution, since it is unlikely that such a connection played a role in the survival of our species tens of thousands of years ago. If God exists, we can give an explanation: God gave us aesthetic preferences that guide us to truth.
The second story is that fundamental necessary reality is itself innately beautiful, and beautiful theories exhibit the beauty of their subject matter. And we recognize this beauty. It is puzzling, though: Why should fundamental necessary reality be beautiful? The best explanation of that which I can think of is again theistic: God is beauty itself, and all necessary truths are grounded in God.
Of course, one might simply reject the claim that our aesthetic preferences between theories lead to truth. But I think that would be the end of much of philosophy.
I think that in the order of knowing, aesthetics and ethics come first or close to first.