Full Idea
It is a highly unphilosophic expedient to resort to a number of proofs for one and the same proposition, consoling oneself that the multitude of reasons makes up for the inadequacy of any one of them taken by itself.
Gist of Idea
Philosophers should not offer multiple proofs - suggesting the weakness of each of them
Source
Immanuel Kant (Metaphysics of Morals II:Doctrine of Virtue [1797], 403 Intro XIII)
Book Reference
Kant,Immanuel: 'The Metaphysics of Morals', ed/tr. Gregor,Mary [CUP 1991], p.204
A Reaction
This makes philosophical proofs sound very mathematical in character, whereas I think most reasons for a proposition given in philosophy are more like evidence, which can clearly accumulate in a rational way. Some maths proofs are better than others.