e, and the soul. In the early years of the seventeenth
century Descartes had sharply distinguished between the two
substances--mind, with its attribute of thought; and body, with its
attribute of extension--and divided the finite world between them. God
was regarded as the infinite and sustaining cause of both. Stated in the
terms of epistemology, the object of clear thinking is the physical
cosmos, the subject of clear thinking the immortal soul. The realm of
perception, wherein the mind is subjected to the body, embarrasses the
Cartesian system, and has no clear title to any place in it. And without
attaching cognitive importance to this realm, the system is utterly
dogmatic in its epistemology.[273:6] For what one substance thinks, must
be assumed to be somehow true of another quite independent substance
without any medium of communication. Now between Descartes and Berkeley
appeared the sober and questioning "Essay Concerning Human
Understanding," by John Locke. This is an interesting combination (they
cannot be said to blend) of traditional metaphysics and revolutionary
epistemology. The universe still consists of God, the immortal thinking
soul, and a corporeal nature, the object of its thought. But, except for
certain proofs of God and self, knowledge is entirely reduced to the
perceptual type, to sensations, or ideas directly imparted to the mind
by the objects themselves. To escape dogmatism it is maintained that
the real is what is _observed to be present_. But Locke thinks the
qualities so discovered belong in part to the perceiver and in part to
the substance outside the mind. Color is a case of the former, a
"secondary quality"; and extension a case of the latter, a "primary
quality." And evidently the above empirical test of knowledge is not
equally well met in these two cases. When I see a red object I know that
red exists, for it is observed to be present, and I make no claim for it
beyond the present. But when I note that the red object is square, I am
supposed to know a property that will continue to exist in the object
after I have closed my eyes or turned to something else. Here my claim
exceeds my observation, and the empirical principle adopted at the
outset would seem to be violated. Berkeley develops his philosophy from
this criticism. His refutation of material substance is intended as a
full acceptance of the implications of the new empirical epistemology.
Knowledge is to be all of the perceptual