Full Idea
Realists feel that the one-place predication 'a is F' leaves something unexplained, yet all that is offered is a two-place predication (a relational statement). There is an equal problem about 'a having F-ness'.
Gist of Idea
Realism doesn't explain 'a is F' any further by saying it is 'a has F-ness'
Source
Michael Devitt ('Ostrich Nominalism' or 'Mirage Realism'? [1980], p.97)
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.97
A Reaction
I think this is a key argument on the nominalist side - the denial that the theory of universals actually makes any progress at all in giving an explanation of what is going on around here. Platonist have the problem of 'partaking'.