Process and Reality — the Gifford Lectures, 1929

put whatever it be, there it is—exhibiting to us a certain region of external space. If we are gazing at a nebula, a thousand light-years away, we are not looking backward through a thousand years. Such ways of speaking are interpretative phrases, diverting attention from the primary fact of direct experience, observing the illumination of a contemporary patch of the heavens. In philosophy, it is of the utmost importance to beware of the interpretative vagaries of language. Further, the extent of the patch illuminated will depend entirely upon the magnifying power of the telescope used. The correlation of the patch, thus seen through the telescope, with a smaller patch, defined by direct ‘projection’ from the observer, is again a question of scientific interpretation. This smaller patch is what we are said to have seen ‘magnified’ by the use of the telescope. What we do see is the bigger patch, and we correlate it with the smaller patch by theoretical calculation. The scientific explanation neglects the telescope and the larger patch really seen, and considers them as merely instrumental intermediaries. It concentrates on the contemporary smaller patch, and finally deserts aven that patch in favour of another region a thousand years in the past. This explanation is only one illustration of the way in which so-called statements of direct observation are, through and through, merely interpretative statements of simple direct experience. When we say that we have seen a man, we may mean that we have seen a patch which we believe to be a man. In this case, our total relevant experience may be more than that of bare sight. In Descartes’ phraseology, our experience of the external world embraces not only an ‘inspectio’ of the ‘realitas objectiva’ in the prehensions in question, but also a ‘judicium’ which calls into play the totality of our experience beyond those prehensions. The objection to this doctrine of ‘presentational immediacy’—that it presupposes a definition of straight lines, freed from dependence on external actualities—has been removed by the production of such a definition in the previous chapter.

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Of course the point of the definition is to demonstrate that the extensive continuum, apart from the particular actualities into which it is atomized, includes in its systematic structure the relationships of regions expressed by straight lines. These relationships are there for perception.

SECTION III

The Cartesian doctrine of the ‘realitas objectiva’ attaching to presentational immediacy is entirely denied by the modern doctrine of private psychological fields. Locke’s doctrine of ‘secondary qualities’ is a halfway house to the modern position, and indeed so is Descartes’ own position considered as a whole. Descartes’ doctrine on this point is obscure, and is interpretable as according with that of the philosophy of organism. But Locke conceives the sensa as purely mental additions to the facts of physical nature. Both philosophers conceive the physical world as in essential independence of the mental world, though the two worlds have ill-defined accidental relationships. According to the philosophy of organism, physical and mental operations are inextricably intertwined; also we find the sensa functioning as forms participating in the vector prehensions of one occasion by another; and finally in tracing the origin of presentational immediacy, we find mental operations transmuting the functions of sensa so as to transfer them from being participants in causal prehensions into participants in presentation prehensions. But throughout the whole story, the sensa are participating in nature as much as anything else. It is the function of mentality to modify the physical participation of eternal objects: the case of presentational prehensions is only one conspicuous example. The whole doctrine of mentality—from the case of God downwards—is that it is a modifying agency. But Descartes and Locke abandon the ‘realitas objectiva’ so far as sensa are concerned (but for Descartes, cf. Meditation I, “It is certain all the same that the colours of

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which this is composed are necessarily real”), and hope to save it so far as extensive relations are concerned. This is an impossible compromise. It was easily swept aside by Berkeley and Hume. (Cf. Enquiry, Part I, Sect. XII. Hume with obvious truth, refers to Berkeley as the originator of this train of argument.) The modern doctrine of ‘private psychological fields’ is the logical result of Hume’s doctrine, though it is a result which Hume ‘as an agent’ refused to accept. This modern doctrine raises a great difficulty in the interpretation of modern science. For all exact observation is made in these private psychological fields. It is then no use talking about instruments and laboratories and physical energy. What is really being observed are narrow bands of colour-sensa in the private psychological space of colour-vision. The impressions of sensation which collectively form this entirely private experience ‘arise in the soul from unknown causes.’ The spectroscope is a myth, the radiant energy is a myth, the observer’s eye is a myth, the observer’s brain is a myth, and the observer’s record of his experiment on a sheet of paper is a myth. When some months later, he reads his notes to a learned society, he has a new visual experience of black marks on a white background in a new private psychological field. And again, these experiences arise in his soul ‘from unknown causes.’ It is merely ‘custom’ which leads him to connect his earlier with his later experiences.

All exact measurements are, on this theory, observations in such private psychological fields.

Hume himself ‘as an agent’ refused to accept this doctrine. The conclusion is that Hume’s account of experience is unduly simplified. This is the conclusion adopted by the philosophy of organism.

But one important fact does emerge from the discussion: that all exact measurements concern perceptions in the mode of presentational immediacy; and that such observations purely concern the systematic geometric forms of the environment, forms defined by projectorsp. 498 from the ‘seat? of the strain and irrespective of the actualities which constitute the environment. The contemporary actualities of the world are irrelevant to these observations. All scientific measurements merely concern the systematic real potentiality out of which these actualities arise. This is the meaning of the doctrine that physical science is solely concerned with the mathematical relations of the world.