Sense-Data

Sense-data is Russell's term that denotes that which we are directly aware of in perception.

Sensation

The mental process of receiving and processing sense-data.

Knowledge by Acquaintance

Knowledge derived from sense-data, be it mental or physical.

Knowledge by Description

Knowledge derived from propositions not known through acquaintance directly.

Induction

The process of inferring knowledge or probable opinion from evidence that is not absolutely certain.

A Priori Knowledge

Knowledge known independently of experience.

Universals

General facts that correspond to types in language. For instance, the term "whiteness" denotes the universal "whiteness" that all white things take part in.

Intuitive Knowledge

Knowledge known directly through intuition or self-evidence.

Truth

The relation that obtains when a proposition is believed and corresponds to facts.

Knowledge

True belief believed for the right reasons.

Philosophy

The practice of inquiring into the most fundamental questions about the nature of existence, knowledge, and the like...