I refute it THUS

How do we know? What is reality? These are the questions which philosophers address, and it is easy for scientists to get tetchy with such BIG questions - we find it difficult to imagine making progress across a such  pathless landscape.  Science has made what progress it has largely by adopting a reductionist view of the world - chipping away at a small-small section of the great wall of knowledge rather than stepping back to try comprehending the whole thing.  It has worked - we have transistors and antibiotics; refrigerators and windfarms; GM food and General Motors - by focusing on one thing at a time.

Berkeley Birthday today!  George Berkeley was born 12th March 1685, went to Trinity College Dublin >!huzzah!<, and finished up as Bishop of Cloyne: a metropolis of 1,500 people in Co. Cork - about the same size as another bishopric nearer to us called Ferns.  In those days, just after the founding of the Royal Society, there was no Arts-Science divide; natural philosophers moved easily between the two, at least partly because there was much less to know back then. As JBS Haldane put it "Keats [b. 1795] and Shelley [b. 1795] were the last two poets who were at all up to date with their chemical knowledge”. Berkeley started his publishing career with a book An Essay towards a New Theory of Vision which described his research into and deep thoughts about light and the reality of objects. He later summed up his thoughts as "esse is percipi"- to be is to be perceived. Things don't exist until and unless someone sees them.  This is obvious nonsense until you start to think about it, and Berkeley forced us to question a lot of our unconsidered certainties about what is out there.  It is summed up, maybe even guyed, with the idea "If a tree falls in the forest and no one is around to hear it, does it make a sound?"  The issue was still exercising people 200 years later when another cleric Monsignor Ronald Knox, Catholic convert and broadcaster penned a pair of limericks:

“There was a young man who said "God
Must find it exceedingly odd
To think that the tree
Should continue to be
When there's no one about in the quad."

Reply:

"Dear Sir: Your astonishment's odd;
I am always about in the quad.
And that's why the tree
Will continue to be
Since observed by, Yours faithfully, God.”

The old curmudgeon Samuel "Dictionary" Johnson had no time for such living-in-your-head piffle.  As related by the world's nicest sychophant James Boswell in his biography of the great man:

"After we came out of the church, we stood talking for some time together of Bishop Berkeley's ingenious sophistry to prove the nonexistence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it -- "I refute it thus."

Yes, yes, but it is more complex than that and it is worth thinking a little on the subject before turning our attention back to checking to TV listings. No better place for that than listening [In Our Time on BBC Radio 4] to Melvin Bragg and his guests being damned clever on our behalf.  U. Cal Berkeley,  preeminent college of the US West Coast, is named for him although pronounced [BURKly] wrong differently.