Full Idea
Those who believe in universals appeal to the meaningfulness of language, the lawlike nature of causation, the inter-subjectivity of thinking, our ability to classify new entities, gradation, and the need for perfect standards or paradigms.
Clarification
'Inter-subjectivity' is the ability of two minds to communicate
Gist of Idea
Evidence for universals can be found in language, communication, natural laws, classification and ideals
Source
J.P. Moreland (Universals [2001], Ch.1)
Book Reference
Moreland,J.P.: 'Universals' [Acumen 2001], p.1
A Reaction
Of these, language and communication ought to be explicable by convention, but classification and natural laws look to me like the best evidence.