(after Plato) the doctrine that abstract entities really do exist (often specialised to some particular domain, e.g. mathematics)

The belief that mathematical objects have an objective existence as abstract objects, independently of us and of the physical world.

The philosophical tradition that, following Plato, postulates the existence of an autonomous realm of Ideas or Forms or essences existing outside space and time and independently of manifestations of them in the phenomenal world.

Philosophical system derived from Plato's writings. The basic teaching of Platonism is that ultimate reality cannot be found in everyday life but in the world of the "Forms." Knowledge of the Forms comes by moral and intellectual purification.