something independent of
perception may be opposed as a reality to an 'appearance', which, as
such, presupposes perception. We can say neither that an appearance is
convergent, nor that the appearance of the lines is convergent. Only a
reality similar to the lines, e. g. two roads, can be said to be
convergent. Our ordinary thought, therefore, furnishes no ground for
the view that the object of perception is not the thing, but merely an
appearance of or produced by it. In the second place, the assertion
that the lines _look_ convergent implies considerable knowledge of the
real nature of the reality to which the assertion relates. Both the
terms 'lines' and 'convergent' imply that the reality _is_ spatial.
Further, if the context is such that we mean that, while the lines
look convergent, we do not know their real relation, we imply that
the lines really possess some characteristic which falls within the
genus to which convergence belongs, i. e. we imply that they are
convergent, divergent, or parallel. If, on the other hand, the context
is such that we mean that the lines only look convergent, we imply
that the lines are parallel, and therefore presuppose complete
knowledge in respect of the very characteristic in regard to which we
state what is only appearance. The assertion, then, in respect of a
primary quality, that a thing looks so and so implies knowledge of its
general character as spatial, and ignorance only of a detail; and the
assertion that a thing only looks or appears so and so implies
knowledge of the detail in question.

Attention may now be drawn to a general difficulty which may be raised
with respect to the use of the terms 'looks' and 'appears'. It may be
stated thus: 'If the lines are not convergent, how is it possible even
to say that they _look_ convergent? Must it not be implied that at
least under _certain_ circumstances we should perceive the lines as
they are? Otherwise, why should we use the words 'look' or 'appear' at
all? Moreover, this implication can be pushed further; for if we
maintain that we perceive the real lines, we may reasonably be asked
whether we must not under _all_ circumstances perceive them as they
are. It seems as though a reality cannot be perceived except as it
is.' It is the view to which this difficulty gives rise which is
mainly responsible for the doctrine that the object of perception is
not the reality, but an appearance. Since we do distinguish between
what thin