Full Idea
The properties of number must be capable of proof without appeal to the general properties of progressions, since cardinals can be independently defined, and must be seen in a progression before theories of progression are applied to them.
Gist of Idea
Properties of numbers don't rely on progressions, so cardinals may be more basic
Source
Bertrand Russell (The Principles of Mathematics [1903], §243)
Book Reference
Russell,Bertrand: 'Principles of Mathematics' [Routledge 1992], p.251
A Reaction
Russell says there is no logical priority between ordinals and cardinals, but it is simpler to start an account with cardinals.