Full Idea
The main objection to Kant's philosophy is that to say that logic and arithmetic are contributed by us does not account for its certainty; if Kant is right, then tomorrow our nature could so change as to make two and two become five.
Gist of Idea
If, as Kant says, arithmetic and logic are contributed by us, they could change if we did
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
One would expect a realist like Russell to have fairly fundamental objections to the implied anti-realism (and conventionalism) of Kant. The same comment could be made about Kant's view of space, time and causation.