Philosophers investigating the nature of knowledge from Bacon and Descartes to logical empiricism, have sought to understand its character by means of the distinction between the content of knowledge, and the abstract logical and mathematical principles which regulate its structure or form. The nature of the distinction, the relative roles of content and form, and the relationships between the two, however, have been given widely divergent interpretations.

In books on the calculus of probability, there have been many accounts as to what is the meaning of the term “probable.” We can readily divide them into three groups. The first sometimes defines probability in terms of the ratio between the number of cases favorable to an event and the number of equally possible cases. Sometimes probability is defined in some way other than this, but the above formulation, or one similar to it is used to describe the “measure of probability.” This concept is what is called “the classical concept” of probability and was held by the great workers in the field of probability from the beginning of the eighteenth and opening of the nineteenth centuries, including James Bernoulli (1713), Thomas Bayes (1763), and the Marquis de Laplace (1812). The second conceives of probability as a logical relation between hypothesis and evidence. Following this conception, one could identify “probability” with “degree of confirmation.” We will term this the “logical concept.” The third group identified probability with the relative frequency with which a property occurs in a specified class of elements. We will call this the “frequency concept.”

May I suggest that there is an angle to the problem of purposeful and non-purposeful behavior which has been overlooked in the recent discussions in this journal (Philosophy of Science, Vol. 17, Nr 4, pp. 310–332), namely, the psychological side of the problem.

The task of the philosophy of science, according to Churchman, is twofold. It is, one, “to determine the ideal of science by scientific methods,” and, the other, “to describe the manner in which science can most efficiently approach its ideals” (190). The primary purpose of this book on experimental inference is to deal with these two subjects as they bear upon what is commonly called material or empirical science, rather than upon formal or analytic science, though it is recognized that no absolute separation can be made between these two different types of science, or between the performance of the above tasks in connection with each. The kind of science, then, whose objective and methods are to be elucidated is the kind in which in some broad sense of these terms decisions are necessarily made on the basis of empirical observation and testing. Some observation or series of observations is made, and it is the task of the scientist to make an inference based upon these observational data. What is his aim in doing this, and what are the most efficient ways in which he can proceed?

Men think in terms of models. Their sense organs abstract the events which touch them; their memories store traces of these events as coded symbols; and they may recall them according to patterns which they learned earlier, or recombine them in patterns that are new. In all this, we may think of our thought as consisting of symbols which are put in relations or sequences according to operating rules. Both symbols and operating rules are acquired, in part directly from interaction with the outside world, and in part from elaboration of this material through internal recombination. Together, a set of symbols and a set of rules may constitute what we may call a calculus, a logic, a game or a model. Whatever we call it, it will have some structure, i.e., some pattern of distribution of relative discontinuities, and some “laws” of operation.

The theory of knowledge is justified only by its results. Each of its statements is essentially an hypothesis, valuable in so far as its practical purpose is fulfilled. Consequently, the same speculative characteristics common to all natural sciences, must be attributed also to the theory of knowledge.

Science is based upon the supposition that planning is essential to and effective in the discovery of truth,—planning within and between the minds of individuals. If planning is so, then the cooperative planning of scientific research in the field of the science of religion would contribute to the discovery of truth. The symposia which the Philosophy of Science Association has authorized be published in its journal and the papers on E. S. P. and upon psychoanalytical theory which it secured for its recent national meeting reveal, it seems to the present writer, that the Association recognizes the value of cooperative planning in the discovery of truth, specifically in the field of the science of religion.