it to be explained or defined? It was not
an error, it was a step in the right direction, when Protagoras said
that 'Man is the measure of all things,' and that 'All knowledge is
perception.' This was the subjective which corresponded to the objective
'All is flux.' But the thoughts of men deepened, and soon they began
to be aware that knowledge was neither sense, nor yet opinion--with or
without explanation; nor the expression of thought, nor the enumeration
of parts, nor the addition of characteristic marks. Motion and rest were
equally ill adapted to express its nature, although both must in some
sense be attributed to it; it might be described more truly as the mind
conversing with herself; the discourse of reason; the hymn of dialectic,
the science of relations, of ideas, of the so-called arts and sciences,
of the one, of the good, of the all:--this is the way along which Plato
is leading us in his later dialogues. In its higher signification it was
the knowledge, not of men, but of gods, perfect and all sufficing:--like
other ideals always passing out of sight, and nevertheless present to
the mind of Aristotle as well as Plato, and the reality to which they
were both tending. For Aristotle as well as Plato would in modern
phraseology have been termed a mystic; and like him would have defined
the higher philosophy to be 'Knowledge of being or essence,'--words to
which in our own day we have a difficulty in attaching a meaning.

Yet, in spite of Plato and his followers, mankind have again and again
returned to a sensational philosophy. As to some of the early thinkers,
amid the fleetings of sensible objects, ideas alone seemed to be fixed,
so to a later generation amid the fluctuation of philosophical opinions
the only fixed points appeared to be outward objects. Any pretence
of knowledge which went beyond them implied logical processes, of the
correctness of which they had no assurance and which at best were only
probable. The mind, tired of wandering, sought to rest on firm ground;
when the idols of philosophy and language were stripped off, the
perception of outward objects alone remained. The ancient Epicureans
never asked whether the comparison of these with one another did not
involve principles of another kind which were above and beyond them. In
like manner the modern inductive philosophy forgot to enquire into
the meaning of experience, and did not attempt to form a conception of
outward objects apart from t