man metaphysicians, is that which he and
others have called the Relativity of Human Knowledge. It is
the subject of the most generally known and impressive of
all his writings--the one which first revealed to the
English metaphysical reader that a new power had arisen in
philosophy. Together with its developments, it composes the
Philosophy of the Conditioned, which he opposed to the
French and German philosophies of the Absolute, and which is
regarded by most of his admirers as the greatest of his
titles to a permanent place in the history of metaphysical
thought. But, "the relativity of human knowledge," like most
other phrases into which the words _relative_ or _relation_
enter, is vague, and admits of a great variety of meanings,'
&c.

Mr Mill then proceeds to distinguish these various meanings, and to
determine in which of them the phrase is understood by Sir W. Hamilton.

One meaning is, that we only know anything by knowing it as
distinguished from something else--that all consciousness is of
difference. It is not, however, in this sense that the expression is
ordinarily or intentionally used by Sir W. Hamilton, though he fully
recognizes the truth which, when thus used, it serves to express. In
general, when he says that all our knowledge is relative, the relation
he has in view is not between the thing known and other objects compared
with it, but between the thing known and the mind knowing--(p. 6).

The doctrine in this last meaning is held by different philosophers in
two different forms. Some (e.g. Berkeley, Hume, Ferrier, &c.), usually
called Idealists, maintain not merely that all we can possibly know of
anything is the manner in which it affects the human faculties, but that
there is nothing else to be known; that affections of human or of other
minds are all that we can know to exist--that the difference between the
ego and the non-ego is only a formal distinction between two aspects of
the same reality. Other philosophers (Brown, Mr Herbert Spencer, Auguste
Comte, with many others) believe that the ego and the non-ego denote two
realities, each self-existent, and neither dependent on the other; that
the Noumenon, or 'thing _per se_,' is in itself a different thing from
the Phenomenon, and equally or more real, but that, though we know its
existence, we have no means of knowing what it is. All that we can know
is, relatively to ourselve