Full Idea
Two physical objects and two other physical objects must make four physical objects, even if physical objects cannot be experienced, so Kant's solution unduly limits the scope of a priori propositions.
Gist of Idea
Two plus two objects make four objects even if experience is impossible, so Kant is wrong
Source
comment on Immanuel Kant (Critique of Pure Reason [1781]) by Bertrand Russell - Problems of Philosophy Ch.8
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.49
A Reaction
The point seems good, though it is doubtful whether Russell is entitled to be so confident. If the basis of a priori certainty is pushed outside the mind, our ontology becomes dramatically more complicated.