It is convenient to divide the theory of knowledge into three sets of
problems: 1. the nature of knowledge, certainty and related notions, 2.
the nature and validi- ty of the sources of knowledge, and 3. answers to
skeptical arguments. The first set includes questions such as: What is
it to know that something is the case? Does knowledge imply certainty?
If not, how do they differ? What are the con- ditions of knowledge? What
is it to be justified in accepting something? The sec- ond deals with
the ways in which knowledge can be acquired. Traditional sources have
included sources of premisses such as perception, memory, in-
trospection, innateness, revelation, testimony, and methods for drawing
conclu- sions such as induction and deduction, among others. Under this
heading, philosophers have asked: Does innateness provide knowledge?
Under what con- ditions are beliefs from perception, testimony and
memory justified? When does induction yield justified belief? Can
induction itself be justified? Debates in this area have sometimes led
philosophers to question sources (e. g., revela- tion, innateness) but
usually the aim has been to clarify and increase our understanding of
the notion of knowledge. The third class includes the peren- nial
puzzles taught to beginning students: the existence of other minds, the
problem of the external world (along with questions about idealism and
phenomenalism), and more general skeptical problems such as the problem
of the criterion. These sets of questions are related.
