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Recent Contributions to
The Mathematical Theory of Communication 

Warren Weaver September, 1949 

Communication 

THE WORD communication will be used here in a very broad sense to include all of the procedures by which one mind may affect another. This, of course, involves not only written and oral speech, but also music, the pictorial arts, the theatre, the ballet, and in fact all human behavior. In some connections it may be desirable to use a still broader definition of communication, namely, one which would include the procedures by means of which one mechanism (say automatic equipment to track an airplane and to compute its probable future positions) affects another mechanism (say a guided missile chasing this airplane). 

The language of this memorandum will often appear to refer to the special, but still very broad and important, field of the communication of speech; but practically everything said applies equally well to music of any sort, and to still or moving pictures, as in television. 

1.2 Three Levels of Communications Problems 

Relative to the broad subject of communication, there seem to be problems at three levels. Thus it seems reasonable to ask, serially: 

LEVEL A. How accurately can the symbols of communication be transmitted? (The technical problem.) 

LEVEL B. How precisely do the transmitted symbols convey the desired meaning? (The semantic problem.) 

LEVEL C. How effectively does the received meaning affect conduct in the desired way? (The effectiveness problem.) 

The technical problems are concerned with the ac- curacy of transference from sender to receiver of sets of symbols (written speech), or of a continuously varying signal (telephonic or radio transmission of voice or mu- sic), or of a continuously varying two-dimensional pat- tern (television), etc. Mathematically, the first involves transmission of a finite set of discrete symbols, the second the transmission of one continuous function of time, and the third the transmission of many continuous functions of time or of one continuous function of time and of two space coordinates. 

propaganda theory, to those value judgments which are necessary to give useful meaning to the words “success” and “desired” in the opening sentence of this section on effectiveness. 

The effectiveness problem is closely interrelated with the semantic problem, and overlaps it in a rather vague way; and there is in fact overlap between all of the suggested categories of problems.