It is too often forgotten that even the most “objective” science such as physics is but a description, interpretation and ordering of physical reality from a selected point of view.

In founding terrestial dynamics, Galileo, the father of modern experimental physics, selected concepts that could be given exact mathematical definitions and cast in a form conducive to quantitative results. The qualitative aspects of observed phenomena, such as the color of an accelerated body, and the ultimate cause of motion—a purely metaphysical problem—do not enter into the mathematical dynamical system of Galileo.

Although generalization is universally relied on in all scientific thought and is prerequisite to it, many students of scientific methods have neglected to analyze generalizing behavior. This is understandable in view of the fact that generalizing thought begins early in childhood and continues at simple or complex levels through the years of elementary school, high school and college. Most such generalization is clearly pre-critical, following the patterns of parents, playmates and teachers by means of suggestion, imitation and insight. In spite of its universality, however, the process of generalization deserves careful analysis in order that it be fully understood and that errors in interpretation of experience due to faulty generalizing may be avoided.

Although a great deal has been written concerning the verifiability of empirical, declarative sentences, yet some further clarification in this area seems possible and desirable. I think it is important to determine what sort of property ‘verified by’ is. Obviously it is a semiotical property. Only sentences, never matters of fact, are verified. But where, in the area of semiotics, is it to be placed? To use Charles Morris's useful and now somewhat traditional classification, is it a syntactic, semantic, or pragmatic (i.e. psychological) predicate? My answer is that it falls within semantics. Before developing this, however, I should like to point out why I do not place it in either of the other two subdivisions.

W. E. Hocking has written recently that Whitehead's descriptive generalization of concrete fact, namely, his actual occasion, is “… not a term of description in the direct sense. It is an hypothesis. It cannot be kept in place by pointing to its presence as a datum: it can only hold its own if it proves to be a valuable conceptual tool.” I further advance the thesis that all generality is hypothetical, and holds it own only if it proves to be conceptually useful. This is in accord with Whitehead's statement, the full implications of which have not been taken seriously enough, that metaphysical categories are not dogmatic statements of the obvious; they are tentative formulations of the ultimate generalities. But when these tentative formulations prove conceptually useful or are conceptually employed, they lose their “hypothetical air,” and often pass into what Whitehead calls a false state of “sober obviousness:”

“An old established metaphysical system gains a false air of adequate precision from the fact that its words and phrases have passed into current literature. Thus propositions expressed in its language are more easily correlated to our flitting intuitions into metaphysical truth. When we trust these verbal statements and argue as though they adequately analysed meaning, we are led into difficulties which take the shape of negations of what in practice is presupposed. But when they are proposed as first principles they assume an unmerited air of sober obviousness.”

The following remarks have been stimulated by Mr. A. J. Ayer's recent essay “The Terminology of Sense Data.” In this paper Mr. Ayer restates several of the points he has made in his book The Foundations of Empirical Knowledge. The context of his argument is that of the traditional distinction between two kinds of things, sense data, percepts, phenomenal or direct given-nesses on the one hand and so-called physical objects on the other. In this context, Mr. Ayer's argument is, to my mind, very admirable; so I do not intend to comment on it. In some other contexts, some of his formulations may, I fear, give rise to misunderstandings; these, naturally, are the points on which I wish to comment. But before specifying them, I had better make sure that we are talking about the same thing by briefly restating several of Mr. Ayer's points. With some of these, if I understand them correctly, I find myself in agreement; the merit of some others I shall presently examine.

In the ultimate analysis, all philosophical differences are verbal. If by some intellectual X-Ray we could see into the minds of others, and perceive the exact nature of their concepts, we should be force to concede the correctness of their conclusions. The only alternative is that the mental processes—the laws of thought—differ from individual to individual.