Full Idea
Santayana remarked that he who is ignorant of the history of philosophy is doomed to repeat it.
Gist of Idea
He who is ignorant of the history of philosophy is doomed to repeat it
Source
report of George Santayana (The Life of Reason [1906]) by Alasdair MacIntyre - A Short History of Ethics Ch.1
Book Reference
MacIntyre,Alasdair: 'A Short History of Ethics' [Routledge 1967], p.3
A Reaction
Santayana's remark seems to have been about history in general, so this is a Macintyre thought. It obviously has a lot of truth, and most great philosophers seem hugely knowledgeable. However, ignorance brings a kind of freedom.