Bertrand Russell

render it impossible for them to turn their heads round: and imagine a bright fire burning some way off, above and behind them, and an elevated roadway passing between the fire and the prisoners, with a low wall built along it, like the screens which conjurors put up in front of their audience, and above which they exhibit their wonders.
I have it, he replied.
Also figure to yourself a number of persons walking behind this wall, and carrying with them statues of men, and images of other animals, wrought in wood and stone and all kinds of materials, together with various other articles, which overtop the wall; and, as you might expect, let some of the passers-by be talking, and others silent.
You are describing a strange scene, and strange prisoners.
They resemble us, I replied.
Now consider what would happen if the course of nature brought them a release from their fetters, and a remedy for their foolishness, in the following manner. Let us suppose that one of them has been released, and compelled suddenly to stand up, and turn his neck round and walk with open eyes towards the light; and let us suppose that he goes through all these actions with pain, and that the dazzling splendour renders him incapable of discerning those objects of which he used formerly to see the shadows. What answer

Descartes (1596-1650), the founder of modern philosophy

perhaps a majority, have held that there is nothing real except minds and their ideas. Such philosophers are called 'idealists'

Cogito, ergo sum

Dialogues between Hylas and Philonous, in Opposition to Sceptics and Atheists

no two can see it from exactly the same point of view, and any change in the point of view makes some change in the way the light is reflected.

If, then, we cannot trust what we see with the naked eye, why should we trust what we see through a microscope? Thus, again, the confidence in our senses with which we began deserts us.

Bishop Berkeley (1685-1753). His Three Dialogues between Hylas and Philonous, in Opposition to Sceptics and Atheists, undertake to prove that there is no such thing as matter at all, and that the world consists of nothing but minds and their ideas.

But science habitually assumes, at least as a working hypothesis, that general rules which have exceptions can be replaced by general rules which have no exceptions

the main reasons why we do not to a greater degree draw the same conclusions from that evidence is that we do not really learn the difficult art of thought