Physics equally independent of experience. And it accounts for the
existence of these.

With Mathematics we are not now concerned, and I will pass them by with
only one remark. The ground on which Kant's theory stands is not
sufficient, for this simple reason. It accounts for one fact; it does
not account for another fact. It accounts for the fact that we attach
and cannot help attaching a conviction of necessity to all mathematical
reasoning. We not only know that two straight lines cannot enclose a
space, but we know that this is so and must be so in all places and at
all times, and we know it without any proof whatever. This fact Kant
accounts for. Space is according to him a part of our kaleidoscope; you
can always look into it and see for yourself what are the laws of it.
But there is another fact. This space of which we are speaking is
unquestionably to our minds not a thing inside of us but outside of us.
We are in it. We cannot get rid of a sense that it is independent of
ourselves. We can imagine ourselves non-existing, minds and all. We
cannot imagine space non-existing. If it be a part of our minds, how is
it that we can picture to ourselves the non-existence of the mind which
is the whole, but not the non-existence of space which, according to the
hypothesis, is the part? For this fact, which we commonly call the
objectivity of space, Kant's theory does not account. In fact Kant
appears to have no escape from assigning this objectivity of space to
delusion. But a theory which requires us to call an ineradicable
conviction of consciousness a delusion cannot be said to explain all the
facts. John Stuart Mill maintains that the other fact, namely, the
conviction of the necessity of mathematical truth, is a delusion. And
his account also must be pronounced for that reason to fail in
accounting for all the facts.