Positivists and phenomenalists of all sorts maintain, and long have maintained, some variant of the following thesis concerning the existence of physical objects: Such statements as ‘There is now a wall behind my back’ are synonymous with a class of statements of which the following is representative ‘If I shall turn my head, then I shall also have the visual experience called ‘seeing a wall'.’ This amounts to proposing what many of us call a philosophical analysis of ‘exist’ or, more (...) precisely, of one meaning of ‘exist'; for the thesis implies that this verb, in the sense in which we use it when we say ‘This wall exists', is dispensable in the sense of being definable. Realists, who oppose the thesis, hold that ‘exist', in the sense mentioned, is what I would call an undefined descriptive predicate; and then they go on to recommend that instead of defining existence in terms of what we see, we had better say that we shall, if we turn, see a wall because there is a wall. Thus one could say, perhaps, that the realists wish to convert the positivistic position; instead of founding existence upon experience, they want to found experience upon existence. To be sure, this is but a bare and crudely formulated schema of an issue that has been argued for a long time. Also, contemporary analysts for the most part do not discuss the issue directly; they give their attention to preliminary and, therefore, more fundamental questions. Like experienced chess players, who know to which characteristic situations in the middle game certain openings will eventually lead, we try to convince each other of the excellence of our respective openings. There is, in particular, one fundamental or opening move that is now widely discussed and which, I believe, most of us examine with a view to the position in which we shall find ourselves—in the middle game—with respect to the realism issue. I refer to the clarification of the relations between meaning and verification or, to put it the way positivists do, to the formulation of an adequate meaning criterion. Let me indicate the connection between these questions and the crude schema I have given for the realism issue. According to current garden varieties of positivism, a statement is meaningful if it is verifiable by experience. ‘There is a wall behind my back’ is, in this view, meaningful because it is synonymous with a class of statements each of which is verifiable by future experience. More pointedly, the familiar common sense statements about the existence of physical objects are considered as meaningful because they are verifiable. This has again the subjectivistic ring realists dislike so much; so they may again be inclined to convert the positivistic position, if only tentatively and because they feel that a piece of realistic common sense would thus be preserved. But to make the conversion is to say that ‘There is a wall behind my back’ is verifiable because it is meaningful. (shrink)

The intention of the present essay is to urge a reconsideration of the Realism-Phenomenalism-Issue, mainly and primarily in regard to the interpretation of scientific hypotheses; secondarily also relating to the basic problems of epistemology.