Parmenides figures out that what is is one. By this he mans eternal and unchanging and uniform. Consequently, all change as well as the external world is an illusion.

Plato figures out our ideas are imitations of eternal, perfect forms. Consequently, knowledge is knowledge of Form,

Berkeley figures out that all that really exists are ideas. Consequently, he proves the existence of a very, very busy God by assigning him the task of holding static all of the ideas of what we formerly called the objects of the external world.

Spinoza figures out that to be truly infinite God must have infinite 'aspects.' Consequently, he infers that although we are only privy to two of these aspects as puny humans- namely extension via the external world and essence via thought- there must necessarily be an infinity of unknowable other 'aspects'.

That's it for today lol.