Full Idea
There is nothing one can imagine so strange or so unbelievable that has not been said by one or other of the philosophers.
Gist of Idea
Almost every daft idea has been expressed by some philosopher
Source
René Descartes (A Discourse on Method [1637], §2.16)
Book Reference
Descartes,René: 'Discourse on Method/The Meditations', ed/tr. Sutcliffe,F.E. [Penguin 1968], p.39
A Reaction
Actually I think that extensive areas of logical possibilities for existence remain totally unexplored. On the other hand, most of the metaphysical beliefs of most of the human race, including the majority of philosophers, strike me as being false.