Idealism

Idealism is the position that reality is fundamentally mental in nature. Different forms of idealism have been developed by Berkeley, Leibniz and Kant.

Berkeleyan idealism

The central thesis of Berkeley's idealism was that only minds and the ideas which they perceive exist. This committed him to immaterialism, the position that there are no material substances, where a substance is something which could exist even if nothing else did. According to Berkeley, objects like trees and chairs existed, but they could not exist independently of being perceived by a mind. He summarised this position with his famous dictum, "Esse est percipi" ("To be is to be perceived").

Transcendental idealism

Immanuel Kant (22 April 1724 – 12 February 1804) defended a view which he called transcendental idealism. Transcendental idealism distinguishes between the phenomenal world of things as we experience them and the noumenal world of things as they are in themselves. Kant considered the properties of the things we experience to be fundamentally subjective.