But great mediaeval philosophers did reflect on what can seem the strange fact that our thoughts and desires and so on are about things. It's clearly not as simple as the first one's being an effect of the second one. In the 17th Century, the French philosopher Rene Descartes set out to find what we can know with absolute certainty, by means of an all-out policy of doubting things. But he also began, as no one else had before him, the idea that your mind and your body are two separate things. Minds think and are not in space.
Bodies are exactly the other way on.
This has since been called dualism. But in that same 17th Century the English philosopher Thomas Hobbes said the opposite, that a mind is just part of the material or physical world. There is no fundamental difference between our minds and our bodies. The Philosophy of Mind in the 20th Century, if it got more complicated than anything said by Hobbes, turned out to be more along his line than Descartes'. The main reason was that philosophers had had too much of mystery.