According to Bertrand Russell, the phrase “theory of knowledge” has two meanings. One kind of theory, the lesser, accepts whatever knowledge science presents and seeks to account for it. Russell’s concern is with the wider kind, which embraces all problems of establishing the nature and validity of all knowledge. Confining his attention in this work to empirical knowledge, he undertakes to discover two things: (1) What is meant by “empirical evidence for the truth of a proposition”? (2) What can be inferred from the fact that there sometimes is such evidence?
Russell brings to the problem of a theory of empirical knowledge the full force of its counterpart, logical knowledge, to whose modern development he is a foremost contributor. He attacks the problems of his general task by translating their elements into formal logical symbols so as to achieve a precision lacking in the language in which the problems are usually couched. Yet the book does not consider problems of logic as such, except when they are relevant to epistemology.
To talk about epistemological matters, Russell sets up a modern linguistic apparatus. He conceives a hierarchy of languages, at whose base is the object-language, or primary language. Terms in the object-language include subjects and predicates. While ordinary language may provide a beginning, every subject of the object-language should be transformed into a unique proper name, making use of coordinates in the visual field and of measures of time for discriminating the object named. The name will apply to a complex; and sometimes names must be given to complex wholes without knowing what their constituents are. People learn the names of things ostensively, and only of those things they actually perceive while hearing or coining their names. The names are employed as subjects in propositions of the simplest sort, called atomic propositions. Their predicates may be designated relations. Letting R stand for the relation “above,” the proposition “A R B” consists of the relation R and the names A and B, and asserts that A is above B. This is a dyadic relation. Predicates may take any number of terms. The predicate of a single name is a monadic relation: “f (A)” states that a characteristic f is an attribute of A.
The secondary language consists of statements about the primary language (and must include the primary language within it). Therefore all words for logical conceptions, such as “is true,” “is false,” “or,” “if,” belong to the secondary language. All logical truths, because they depend for their truth on rules of syntax, are at least on this level, if not higher. An important group of propositions of the secondary language are those stating propositional attitudes, such as “A believes proposition p.”
The distinctive feature of empirical rather than logical truth is, of course, its basis in percepts, the sense images by which perception is possible. Russell adapts A. J. Ayer’s phrase “basic propositions” to designate those propositions arising as immediately as possible from percepts. A basic proposition “is a proposition which arises on occasion of a perception, which is the evidence for its truth, and it has a form such that no two propositions having this form can be mutually inconsistent if derived from different percepts.” Examples in ordinary language are “I am hot,” “That is red.” Many basic propositions may arise describing a single percept, for people perceive a sensory whole combining the entire fields of vision, touch, and so on; and within this field people identify smaller wholes of sensory complexes—the individual objects of the world. Basic propositions need not be atomic propositions. An important group includes some propositions stating propositional attitudes—”I believe proposition p”—and thus basic propositions may occur in the secondary language as well as in the primary.
Unlike most prior writers, Russell does not affirm that basic...
(The entire section is 3,422 words.)