Full Idea
Poincaré once exclaimed, 'Convention, yes! Arbitrary, no!'.
Gist of Idea
Convention, yes! Arbitrary, no!
Source
report of Henri Poincaré (talk [1901]) by Hilary Putnam - Models and Reality
Book Reference
'Philosophy of Mathematics: readings (2nd)', ed/tr. Benacerraf/Putnam [CUP 1983], p.430
A Reaction
An interesting view. It mustn't be assumed that conventions are not rooted in something. Maybe a sort of pragmatism is implied.