HOW FAR CAN PURE LOGIC TAKE US?

HOW FAR CAN PURE LOGIC TAKE US? I find that I now think of the discipline of philosophy as an investigation of how much we can learn from pure logic—without using any facts. The answer seems to me to be that we can’t go any distance at all. Philosophers often wind up with systems which reject the usefulness or even the existence of facts. Plato and Descartes serve as examples. Berkeley winds up at a similar place: the objects of the world are inventions of the mind.