Full Idea
Arguments in philosophy rarely take the form of proofs; and the most successful arguments on topics central to philosophy never do. (The ideal of proof is a relatively barren one in philosophy).
Gist of Idea
Proof is a barren idea in philosophy, and the best philosophy never involves proof
Source
Alasdair MacIntyre (After Virtue: a Study in Moral Theory [1981], Ch.18)
Book Reference
MacIntyre,Alasdair: 'After Virtue: a Study in Moral Theory' [Duckworth 1982], p.241
A Reaction
He seems proud of this, but he must settle for something which is less than proof, which has to be vindicated to the mathematicians and scientists. I agree, though. Plato is the model, and the best philosophy builds a broad persuasive picture.