According to Plato, an ‘idea’ is the general start of something that doesn’t take place in this world, but in the ‘world of ideas’, the highest of all worlds. All visual things on earth, like people, animals, plants, but also for example ethic standards, are reflections of the world of ideas hence mortal and of temporary nature.

The idea ‘mankind’ only exists in the world of ideas; the people that live on earth are reflections of it. All good deeds on earth are reflections of ‘the goodness’ or ‘the idea goodness’. The idea itself isn’t visual, but can only be seen through survey by the intellect, the spirit. Also, according to Plato there is a hierarchy of ideas, in which the idea of goodness comes highest.

Unlike Plato, his pupil Aristotle declared that not the idea was real, but the separate things. An idea is not a thing, it doesn’t even exist; it’s a name. According to Aristotle ‘mankind’ does not exist, it’s an abstraction that only exists in our thoughts, yet doesn’t appear in reality. What does exist is every concrete human being.

Descartes introduced a new problem in the doctrine of ideas. He talked of innate ideas. ‘I know what goodness, truth etc. are, because they were in my nature from the very beginning. The fact I have the idea ‘God’ doesn’t mean I have taught myself this, but that I was born with it.’

Locke completely disagreed with Descartes’ point of view. According to him all thoughts and visions originated in man’s perception. He explained more about this theory in ‘Essay concerning human understanding’, with which he became the founder of empiricism.

Platos visions are still being defended, mostly by American philosophers who rely on the status of mathematical notions. R. Rucker, for example, wrote ‘Infinity and the Mind’ in 1982.