anent subject, the other to the
variable object, without thereby knowing what each would be if it could
be discerned apart from the other. "A direct intuition of things in
themselves," according to Kant and Hamilton, is an intuition of things
out of space and time. Does Mr. Mill suppose that any natural Realist
professes to have such an intuition?

The same error of supposing that a doctrine of relativity is necessarily
a doctrine of Idealism, that "matter known only in relation to us" can
mean nothing more than "matter known only through the mental impressions
of which it is the unknown cause,"[AC] runs through the whole of Mr.
Mill's argument against this portion of Sir W. Hamilton's teaching. That
argument, though repeated in various forms, may be briefly summed up in
one thesis; namely, that the doctrine that our knowledge of matter is
wholly relative is incompatible with the distinction, which Hamilton
expressly makes, between the primary and secondary qualities of body.

[AC] The assumption that these two expressions are or ought
to be synonymous is tacitly made by Mr. Mill at the
opening of this chapter. He opens it with a passage from
the _Discussions_, in which Hamilton says that the
existence of _things in themselves_ is only indirectly
revealed to us "through certain qualities _related to
our faculties of knowledge_;" and then proceeds to show
that the author did not hold the doctrine which these
phrases "seem to convey in the only substantial meaning
capable of being attached to them;" namely, "that we
know nothing of _objects_ except their existence, and
the impressions produced by them upon the human mind."
Having thus quietly assumed that "things in themselves"
are identical with "objects," and "relations" with
"impressions on the human mind," Mr. Mill bases his
whole criticism on this tacit _petitio principii_. He is
not aware that though Reid sometimes uses the term
_relative_ in this inaccurate sense, Hamilton expressly
points out the inaccuracy and explains the proper
sense.--(See _Reid's Works_, pp. 313, 322.)

The most curious circumstance about this criticism is, that, if not
directly borrowed from, it has at least been carefully anticipated by,
Hamilton himself. Of the distinction between primary and secondary
qualities, as acknowledged by Descartes and Locke,