assertion is made in regard to a red wall, then it is obviously untrue.
Our sense impressions give rise to a great variety of such expressions.
We state "the wall is blue" as a result of an impression obtained
through the organs of sight; then we speak of a pungent smell, a sweet
taste, a harsh sound, or a rough stone, on account of impressions
received respectively through the organs of smell, taste, hearing, and
touch. But, of course, all such assertions are superficial in
character--there is little more in them than the application of a
conventional term to an observed phenomenon, they avail us little in
solving the mysteries of the universe.

Strictly speaking, this is for the empiricist the limit of possible
knowledge, but he would be a poor investigator who would be content with
this and no more. The empiricist tries to go a distinct step in advance
of this. The scientist observing the path of a planet travelling round
the sun, finds that its course is that of an ellipse. He studies the
path of a second planet, and finds that this also travels along an
elliptical orbit. Later he finds that all planets he is able to observe
travel in the same kind of path--then he hazards a general statement,
and says, "All planets travel round their suns in elliptical orbits."
But now he has left the realm of certainty for that of uncertainty.
There may be innumerable planets which he cannot observe that take a
different course. He hazards the general statement, because he assumes
(sometimes without knowing that he does so) that nature is uniform and
constant, that it will do to-day as it did yesterday, and does in
infinite space as it does in the visible universe.

The knowledge that is possible to the empiricist, then, is merely that
which is derived from direct experience, and simple summations or
generalisations into a single assertion of a number of similar