Do not exist in and of themselves, but are the product of the way we represent things", because we can know objects only as they appear to us.

The problem of how we can know the existence and nature of the world external to our mind is one of the oldest and most difficult in philosophy. The discussion by John Locke (1632-1704) of knowledge of the external world have proved to be some of the most confusing and difficult passages of his entire body of philosophical work. Difficulties develop on several fronts.