George Berkeley

Berkeley is the foundational modern idealist in the Anglophone tradition. The thesis that only minds and ideas exist is his.

"Esse est percipi." ("To be is to be perceived." — Principles of Human Knowledge §3)

Berkeley is a thoroughgoing British empiricist — all knowledge derives from sense-ideas, just like Locke and Hume. He differs from Locke in denying material substance behind the ideas.

"Whatever is is in the mind." (Principles, summarizing the empiricist starting point pushed to idealist conclusion)

The framework groups confessional Protestant Christianity here. Berkeley was an Anglican bishop; the substantive metaphysics is offered as a defense of Christianity against materialist atheism (the Principles' subtitle: "the chief causes of error and difficulty in the sciences, with the grounds of scepticism, atheism, and irreligion, are inquired into").

"The mind of God is the most intimate ground of all our perceptions." (paraphrasing the substantive theological motivation)

Berkeley is the proximate ancestor of phenomenalism (Mill's "permanent possibilities of sensation" inherits the structure without the theistic underpinning).

"The objects of sense exist only when they are perceived; the trees therefore are in the garden, or the chairs in the parlour, no longer than while there is somebody by to perceive them." (Principles §3)

Berkeley's argumentative method — careful conceptual analysis of what perception involves, leading to a counter-intuitive ontological conclusion — is one of the founding instances of what becomes analytic metaphysics.

"I am content to put the whole upon this issue: if there be anything which is not perceived, you can let me know what it is, and I will give up the cause." (Three Dialogues)