Immanuel Kant came up with a wonderful idea. Let's just say, he writes, that we can't see things "in themselves" but only as appearances. In that one idea he elegantly avoids claiming that we can ever know the whole truth about life, the universe and everything.
Kant's idea is, of course, not much different from St. Paul's talk about seeing through a glass, darkly. And it is echoed by the quantum mechanical dictum that you can't see anything in the sub-atomic world without disturbing it. So you do not see an item "in itself" but only after you have nudged it, with some kind of electromagnetic or sub-atomic energy. So whatever you are looking at, it is not the same as it was.
But Kant feels the need to demolish his predecessors with his Refutation of Idealism. He wants to dispatch the Dogmatic Idealism of Berkeley and the Problematic Idealism of Descartes.
Problem is that most everyone agrees that Kant doesn't quite pull it off, thus violating the first rule of politics that if you come to overthrow the king you had better succeed. Or else.
Kant wants to refute the Cartesian idea that the outer world is "doubtful and indemonstrable." Kant crosses over Descartes' division between knowledge of internal and external states by setting out to prove that the "empirical consciousness of my own existence proves the existence of objects in space outside me." Kant's argument is based on the idea that I am conscious of my existence in time and the presupposition of something "persistent in perception" and so on.
The commentators all seem to agree that Kant doesn't finish the job. Actually, they begin with contesting the first premise of his proof: "I am conscious of my existence as determined in time." They say he doesn't even start the job of refutation properly.
Even a tyro like me can see the problem. Way back in the Transcendental Aestshetic Kant declares that time is a form of intuition that resides in the mind. So we are using an intuition cooked up in the mind to argue for the existence of the real world? Come on Immanuel. You can do better than that! You are really arguing Descartes' point that the only thing we can be sure about is the thinking "I"!
Really, Kant should stick with the beauty and the elegance of his central creative insight. We can't know things in themselves. Everything we know about anything (including our internal self) is founded on belief. We believe in an "I"; we believe in an external world. And until our brains start to rot in old age, that belief seems to work for us. It gets us food, shelter, and a new generation on the ground and out of the nest.
There's a refutation of idealism for you: grandchildren!