As we saw with Empiricism in the last unit, one of its main problems is how check which of our perceptions are true. This problem arises because, for the Empiricist, only what is experienced is real. Therefore, our knowledge of objects comes not from mathematical or logical principles - as it does for the Rationalist - but from direct experience.

So, the fact that we know things about objects in the world is primarily because we have experienced them. All knowledge of physical laws or scientific truths comes through our observation of things which seem to correspond or validate such knowledge. This view has given birth to 3 main theories of perception: Realism, Idealism and Phenomenalism.

We shall now look at each of these in turn.