Full Idea
The identity of a mathematical object may sometimes be fixed by its relation to what lies outside the structure to which it belongs. It is more fundamental to '3' that if certain objects are counted, there are three of them.
Gist of Idea
The identity of a number may be fixed by something outside structure - by counting
Source
Michael Dummett (Frege philosophy of mathematics [1991], Ch. 5)
Book Reference
Dummett,Michael: 'Frege: philosophy of mathematics' [Duckworth 1991], p.53
A Reaction
This strikes me as Dummett being pushed (by his dislike of the purely abstract picture given by structuralism) back to a rather empiricist and physical view of numbers, though he would totally deny that.