Finally, a major issue in Problems of Philosophy lies
in the fact that, to Russell, all knowledge is built on knowledge
by acquaintance, or the things we know through direct, personal
experience. Russell accepts a fundamentally Cartesian point of view,
which means he accepts that the proper foundation for philosophical inquiry
is individual consciousness and perspective. But how can a theory
of knowledge be built on private experiences if this theory is supposed
to apply to all beings? This problem (among others) bothered Russell,
and in his next major epistemological work, Our Knowledge
of the External World, he begins to push his inquiry into the
public sphere.
