George Berkely (1685 – 1753)
Also known as Bishop Berkeley, was an influential Irish philosopher whose primary philosophical achievement is the advancement of a theory he called "immaterialism".
In the second Dialogue Philonous sums up the discussion, so far as it has gone, in the words: “Besides spirits, all that we know or conceive are our own ideas.” He ought not, of course, to make an exception for spirits, since it is just as impossible to know spirit as to know matter. The arguments, in fact, are almost identical in both cases.
When Bishop Berkeley said 'there was no matter,'
And proved it — 'twas no matter what he said.
I come now to Berkeley’s empirical arguments. To begin with, it is a sign of weakness to combine empirical and logical arguments, for the latter, if valid, make the former superfluous. [Footnote: E.g., "I was not drunk last night. I had only had two glasses; besides, it is well known that I am a teetotaller."] If I am contending that a square cannot be round, I shall not appeal to the fact that no Square in any known city is round. But as we have rejected the logical arguments, it becomes necessary to consider the empirical arguments on their merits.
Berkeley was... the first to treat the subjective starting-point really seriously and to demonstrate irrefutably its absolute necessity. He is the father of idealism.