Full Idea
We could not stand in any causal or nomic relation to a realm of propositions over and above the space-time world, ...so it is unclear that such a postulation is of any explanatory value.
Gist of Idea
A realm of abstract propositions is causally inert, so has no explanatory value
Source
David M. Armstrong (Truth and Truthmakers [2004], 02.6)
Book Reference
Armstrong,D.M.: 'Truth and Truthmakers' [CUP 2004], p.12
A Reaction
I agree, and I like Armstrong's appeal to explanation as a criterion for whether we should make an ontological commitment here. I am baffled by anyone who thinks reality is crammed full of unarticulated propositions. Only a philosopher....