ontology

ontology - n - The branch of metaphysics that studies the nature of existence or being as such.

I was - and occasionally still am - deeply interested in philosophical questions. The question ontology deals with is, "What is reality?" Bishop George Berkeley (1685-1753) thought reality was no more than sensual impressions projected on our senses from God's mind, a notion that holds up surprisingly well against attempts at refutation. Ronald Knox wittily summarized Berkeley's thought in two limericks:

There was a young 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."

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