Full Idea
No objective grounds are known to me which permit us to draw a sharp boundary between the two groups of terms, the logical and the non-logical.
Gist of Idea
There is no clear boundary between the logical and the non-logical
Source
Alfred Tarski (works [1936]), quoted by Alan Musgrave - Logicism Revisited §3
Book Reference
-: 'British Soc for the Philosophy of Science' [-], p.103
A Reaction
Musgrave is pointing out that this is bad news if you want to 'reduce' something like arithmetic to logic. 'Logic' is a vague object.