Full Idea
Socrates and Plato are similar if they are both white. Yet the mind can express this either by an 'absolute concept' (as 'Socrates is white' and 'Plato is white'), or by a 'relative concept', as 'Socrates is similar to Plato with respect to whiteness.
Gist of Idea
Relations are expressed either as absolute facts, or by a relational concept
Source
William of Ockham (Seven Quodlibets [1332], VI q.25), quoted by John Heil - The Universe as We Find It 7
Book Reference
Heil,John: 'The Universe as We Find It' [OUP 2012], p.135
A Reaction
Presumably he takes the facts of the matter to be the absolute concept, and the relative concept to be a contribution of the intellect.