Information Processing Theory 39 



If the curve is plotted on log-log coordinates, this rectangular 

 hyperbola becomes a straight line with slope of minus one. The 

 above equation is equivalent to 



nf = K, 

 where 



/ = frequency of occurrence, 

 n = number of words of that frequency, and 

 K = Constant. 



This form is the more usual representation of a frequency dis- 

 tribution. 



The first explanation of this regularity which I wish to discuss 

 is due to Zipf (8), and exemplifies what I will call a mentalistic 

 theory, although I shall try to avoid defense of that term. The 

 basis of Zipf's explanation is the Principle of Least Effort, which 

 itself requires explanation. People, says Zipf, behave so as to 

 minimize effort, and this strategy underlies behavior of all forms. 

 He is at pains to emphasize that effort includes not only actual 

 work but mental effort as well, including the mental effort to 

 decide which path involves the least effort. And here is where the 

 trouble begins. Since a person is unable to predict the future 

 exactly, he must make guesses. The Principle then becomes the 

 statement that a human will behave so as to "minimize the average 

 rate of probable work." At this point it is clear that no problems 

 are solved by the Principle because, in order to make a prediction, 

 we must determine the subject's view of the world and understand 

 his decision process, which of course was the problem with which 

 we began. 



Since this is an important point, let me state it somewhat 

 differently. Although Zipf provides elaborate discussion of what 

 he means by effort, he never gets around to telling us how it is 

 to be measured, nor does he ever rigorously state what is meant 

 by this Principle of Least Effort. Since the length of time over which 

 this undefined effort is to be averaged is also unspecified, it is 

 clear that we can adjust the foresightedness of our subjects to 

 obtain whatever results we desire. Since the word "probable" is 

 thrown in, our only recourse is to the subjective probabilities 

 of the subjects in order to apply the principle; and subjective 



