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".
There once was a man who said, 'God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there's no one about in the Quad.'
I entirely agree with you, as to the ill tendency of the affected doubts of some philosophers, and fantastical conceit of others. I am even so far gone of late in this way of think, that I have quitted several of the sublime notions I had got in their schools for vulgar opinions. And I give it you on my word, since this revolt from metaphysical notions to the plain dictates of nature and common sense, I find my understanding strangely enlightened, so that I can now easily comprehend a great many thing which before were all mystery and riddle.
George Berkeley ... is important in philosophy through his denial of the existence of matter—a denial which he supported by a number of ingenious arguments. He maintained that material objects only exist through being perceived. To the objection that, in that case, a tree, for instance, would cease to exist if no one was looking at it, he replied that God always perceives everything; if there were no God, what we take to be material objects would have a jerky life, suddenly leaping into being when we look at them; but as it is, owing to God’s perceptions, trees and rocks and stones have an existence as continuous as common sense supposes. This is, in his opinion, a weighty argument for the existence of God.
Seeing therefore they are both [heat and pain] immediately perceived at the same time, and the fire affects you only with one simple, or uncompounded idea, it follows that this same simple idea is both the intense heat immediately perceived, and the pain;and consequently, that the intense heat immediately perceived, is nothing distinct from a particular sort of pain.