An instrument is any object which makes possible the attainment of desired ends. It is not essential to the being of the instrument that it be inanimate, worked over, or its mode of operation understood. A pigeon can carry a message; a stone as well as a hammer can be employed to break a glass; a child can start an automobile. The instrument need not function in the interests of men, be set into operation by living beings, or even be used at all. Leaves serve some insects as umbrellas do men; the rays of the sun may turn a screw; a new knife has not yet had a chance to cut. A cow is an instrument for the production of milk, a hen for the production of eggs, though neither is inanimate, worked over, nor its operation understood; they can serve the interests of other animals, are able to initiate their own movements, and may not yet have had occasion to produce the desired results. But they are instruments because they are acknowledged means for the production of the desired milk and eggs.

In undertaking a discussion of the postulates of empiricism, I am confronted by the necessity of being empirical concerning the very postulates themselves. Were those postulates directly accessible to the average mind it would hardly be necessary to enter upon an analysis the success of which seems but a remote possibility even to one who has spent years in the effort to trace the priceless ingredient of the method of experiment in the cheap madness of scientific success. How these postulates reveal themselves to more than the average mind would, of course, be very difficult for me to surmise, except by an ambitious extrapolation. It would have to be an extrapolation of the kind which telescopes a multitude of small rational steps into one swift unerring instinctive flight to the goal of goals. Yet, though genius with one intuitive glance may perceive the postulates as revelation—why not grant that there may be seers who can contemplate eternal objects unblinkingly?—it would still have to descend to mundane means to inform the average mind of its transcendental perceptions. Must not everyone indeed attend to the demands of the average mind?

Human skin is the one authentic criterion of the universe which philosophers recognize when they appraise knowledge under their professional rubric, epistemology. By and large—except for a few of the great Critics and Sceptics—they view knowledge as a capacity, attribute, possession, or other mysterious inner quality of a “knower”; they view this knower as residing in or at a “body”; they view the body as cut off from the rest of the universe by a “skin”; all of which holds for philosophizing physicists and physiologists even as for the professionals of the arcanum itself. If this assertion seems crude, one may recall that there are times when a bit of crudity is a fair physic for an inflamed subtlety. In the case before us the factual crudity lies in the use of “skin” for a criterion, not in our calling attention to the fact. The “skin” that is so used is, indeed, that of ancient anatomical schematism, unaffected by the transformation of understanding which modern physiological research has brought about. Yet if philosophers cease thus crudely to employ it, all their issues of epistemology will vanish, and the very type of attack they make on cognition will be discredited; whereupon the task of determining the status of knowledge itself will pass from their hands to those of the scientists who have taken over so many regions of philosophical arrogation in the past. This is what I propose here to show.

A devoted colleague often asks me: “But what is your philosophy? Are you a monist, dualist, rationalist, idealist, a Kantian? Do you believe Plato was right? Do you think there is free will ?” He is amused by my answer that I do not know what any of those questions mean, that at least I am sufficiently uncertain to avoid venturing an answer. He smiles knowingly and says: “You won't tell.”

The belief in the old type of a priori knowledge is gone. Cartesian innate ideas vanished with the severe criticism of Kant who held that only the form, not the content, of experience is known a priori. More recent criticism of Kant's a priori has taken place indirectly by way of the development of non-Euclidian geometries so that today there is no longer the belief that either the content or the form of experience is fixed and changeless or known with certainty a priori. But has the a priori phase of experience passed altogether? If not, what in recent thought has taken its place?

According to the Laplacian definition, the probability of an event is the ratio of “favorable” cases to possible cases. It is obvious that the definition presupposes the equal probability of the possible cases; and to make the definition of probability depend upon the conception of equal probability has the appearance, at least, of a vicious circle. Moreover it is hard to see how we can assure ourselves that each possible case is really no more and no less probable than any other. But even if we define probability as the relative frequency of occurrence of events under a given set of conditions, or of true conclusions from premises of a given type, we still require the conception of equal probability, unless indeed we choose to renounce entirely the mathematical expression and calculation of probabilities.

I suppose it is generally agreed that the task of science is to render intelligible, or in some way account for, the objects and events of our experience. Usually we say that the job of science is to explain. While this is a satisfactory formulation for most purposes, it hides a difficulty. What is meant by “explanation”? The many interpretations of this word divide scientists and philosophers of science into sharply differentiated schools. For some “explanation” means answering the question, Why?; for others it means merely describing. For some it means finding causes; for others it means finding effects or abandoning entirely the search for causes and effects. For some it means employing quantitative methods only; for others it means supplementing or replacing quantitative methods by qualitative. For some it means interpreting or understanding; for others it means merely adjusting oneself in a practical way.

To one not philosophically inclined, idealism seems a rather fantastic doctrine—one quite obviously false. The great Dr. Johnson thought he could adequately refute it by kicking his toe against a stone. In one form or another, however, it has existed wherever men have thought deeply on the fundamental nature of mind and of the external world. One cannot go far in a study of the sources of knowledge without becoming aware that the only immediate evidence of external objects lies in our sense impressions. The mind has no way of putting itself in contact with things external to itself except through the five senses. Up to this point there is fairly general unanimity. The difficulty lies in correctly interpreting this fact.

The problem of this paper is the discovery of criteria to identify conventions and the description of some of the more general properties of conventions with particular reference to scientific inquiry. Numerous specialized methodological investigations testify to the importance of conventions in inquiry, but none provide a general account of their operation. This paper aims to provide a necessary, if not sufficient, basis for such an account. The discussion falls into three parts: (I) common senses of the term ‘convention’, (II) a provisional formulation of conditions under which a certain type of behavior, which we shall call conventional, occurs, as well as a description of its characters, and (III) a brief consideration of one context of inquiry in which it appears.

The theory of the conservation of energy and the Second Law of Thermodynamics have been described as the two most firmly established “findings” of modern science. Scientists frequently refer to them, not as theories or assumptions, but as facts. During the last two decades of the nineteenth century, however, Edmund Montgomery—an unsung Texas philosopher—repeatedly challenged, not only the notions that energy is convertible and is indestructible, but the very idea that there is such a thing as energy which can be imposed ab extra upon matter. For his trouble he received censure and ridicule on every hand; friends usually apologized for this eccentricity of his. Montgomery, of course, has not been entirely alone in criticizing the theory of the conservation of energy, though he was the first to make a persistent attack on the merits of the theory as a principle of scientific explanation. Busse, for one, contended that if, as he thought likely, the theory were incompatible with psychophysical interactionism, it should be discarded on the grounds that the evidence in its behalf is far from compelling. Emergent evolutionists remind us occasionally that it is still within the province of reason to question this great dogma notwithstanding the fact that it is a god at whose feet many scientists worship with blind and jealous devotion. Of all these critics Montgomery attacked the theory where its greatest weaknesses lie.

When phenomenology was introduced as a new science by Husserl its methods were applied first to objects of logic. Later phenomenological investigation expanded gradually to the fields of psychology, ethics, esthetics, and sociology (Scheler, Pfänder, Hildebrand a.o.). More rarely, objects of the natural sciences have been treated phenomenologically. Scattered indications of this kind are to be found in authors who do not belong to the most intimate circle of Husserl's school (Helmut Plessner, Kurt Goldstein, Walter Frost, E. Buenning). Extensively, however, the phenomenological method has been applied to objects of the natural sciences once only, namely by Hedwig Conrad-Martius, a favorite pupil of Husserl's, in her Realontologie (Ontology of Reality) and Farben (Colors). Yet this less known branch of phenomenology is particularly interesting. Husserl stressed the basic difference between phenomenological ideation (Wesensschau) on the one hand and psychological introspection and description of the immediate data of awareness on the other. The peculiarity and scientific productivity of phenomenological method, therefore, can be studied best in a field which is as far removed from psychology as possible. We shall try to analyze the papers of Conrad-Martius more fully and shall refer to other authors occasionally as illustrations.

Most discussions of Dewey's Logic evade what I take to be its main characteristic. This is its crass display of our intellectual activity as a going process—as living inquiry—literally, biologically, as life. It is the blunt, forthright treatment of even our most formal logical procedures as events occurring within that new world of knowledge that Darwin opened up and that Peirce sketched in his fallibilism, his pragmaticism, and his late-life efforts to attain a functional logic. Lacking are the trailing clouds of logical and philosophical glory; present is only the bare body of inquiry.

From the desire to find support and confirmation for our personal sensory observations, and from the human interest in sharing our experiences with others, there emerges a basic principle of scientific method: We demand the possibility of intelligible communication and agreement concerning individuals' sensory perceptions in particular and their experiences in general. This requirement is made both for the natural and social sciences. The raw material offered for logical organization must be capable of exhibiting an inter-subjective character—such material, or protocols, must be acceptable in common to all concerned. And it must be acceptable for logical organization or systematization in some science.

It is my purpose to examine this law in those cases in which it is generally held to be untrue. I inquire what can be meant, in each case of a statement p considered, by denying the law, that is, by saying ‘Neither p nor —p‘. After separating the possible meanings of this declared indeterminacy, I go on to inquire, taking each possibility in turn, whether the law does in fact fail.

While the members of the school of Logical Empiricism may differ in various details, nearly all of them are opposed to metaphysics on the ground that a scientific metaphysics is the only possible one. All philosophy is to become scientific. This assumption is based on their epistemological criterion of verifiability which appears to be a basic doctrine of this school. The implications of this doctrine have not been worked out in detail by many, but one of the most explicit accounts has been given by A. J. Ayer in his book on Language, Truth and Logic, which can be taken as a representative work in its attack on metaphysics.

In my last talk I introduced you to the system of the sciences and then went on to chat about the first of the natural series of the sciences, namely physics. To-night I shall discuss the other partner of the pair which could be called “the physical sciences”, namely chemistry.

Of both of these sciences, physics and chemistry, it may be said that they are preeminently the study of matter-in-motion. Of both it may be said that the methods of study in the laboratory have a strong resemblance.

If we are to accept the results of modern physics and the significance ascribed to them by eminent exponents of this most exact of all natural sciences, we are in the midst of an important transformation of our conception of the universe. The notion that the law of causality absolutely determines all events has been shaken, and if this law is not to be entirely eliminated from scientific thinking, its formulation must at least be essentially modified. In the course of this controversy the question arises as to the source of the belief that events are determined by an absolute law, that is, the origin of the assumption, which we take for granted, that each event must be the necessary effect of a cause according to an inviolable law. We must try to show how the belief in causality has arisen in the evolution of human thought.

The contentions of this paper are essentially two. One is that truth does not consist of verifiability—and still less of verification—in the sense in which this has been maintained by some pragmatists, operationalists, and positivists. The other is that in a certain other sense of “verifiability”, which will be described, truth is the same thing as verifiability. The paper, it should be understood, attempts only to make clear what is and what is not the relation between truth and verifiability. It does not attempt in addition to carry the analysis of verification itself to the point where it would, by implication, furnish a terminal answer to the question, what is truth. The latter task, because of space limitations, must be reserved for some future occasion.

The following analysis has been undertaken mainly for the purpose of presenting a sample of a method which, as the writer holds, would, if widely and consistently applied, tend considerably to reduce the number and the significance of epistemological problems. The presuppositions characteristic of this method might be summarized in these five statements:

1. 1) You cannot make discoveries by changing the meaning of terms.

2. 2) There is wisdom in common sense since it represents the accumulated experience of the race.

3. 3) It cannot be impossible to work out common sense into a consistent terminology.

4. 4) It is when we lack the patience to do this that epistemological problems seem to arise.

5. 5) But when such a terminology is worked out, it will prove rather disappointing since it will just express, in a somewhat clarified form, what all the world has always been aware of.