number, so that no one of them contains all M’s con- temporaries.
Thus the past of a duration D includes the whole past of any actual occasion belonging to D, such as M for example, and it also includes some of M’s contemporaries. Also the future of the duration D includes the whole future of M, andalso includes some of M’s contemporaries.
So far, starting from an actual occasion M, we find six loci, or types of loci, defined purely in terms of notions derived from ‘causal efficacy.’ These loci are, M’s causal past, M’s causal future, M’s contemporaries, the set of durations defined by M; and finally, taking any one such duration which we call D as typical, there is D’s past, and D’s future. Thus there are the three definite loci, the causal past, the causal present, and the contemporaries, which are defined uniquely by M; and there are the set of dura- tions defined by M, and the set of ‘durational pasts’ and the set of ‘durational futures.’ The paradox which has been introduced by the modern theory of relativity is twofold. First, the actual occasion M does not, as a gen- eral characteristic of all actual occasions, define a unique duration; and secondly such a unique duration, if defined, does not include all the contemporaries of M.
But among the set of durations, there may be one with a unique association with M. For the mode of presenta- tional immediacy objectifies for M, the actual occasions within one particular duration. This is the ‘presented duration.’ Such a presented duration is an inherent fac- tor in the character of an ‘enduring physical object.’ It is practically identical with the strain-locus. This locus is the reason why there is a certain absoluteness in the notions of rest, velocity, and acceleration. For this pre- sented duration is the spatialized world in which the physical object is at rest, at least momentarily for its occasion M. This spatialized world is objectified for M by M’s own conditioned range of feeling-tones which have been inherited from the causal past of the actual occasion
Strains 489
in question, namely, of M. Thus the presented duration is with peculiar vividness part of the character of the actual occasion. A historic route of actual occasions each with its presented duration, constitutes a physical object.
Our partial consciousness of the objectifications of the presented duration constitutes our knowledge of the pres- ent world, so far as it is derived from the senses. Remem- bering that objectifications constitute the objective conditions from which an actual occasion (M/) initiates its successive phases of feeling, we must admit that, in the most general sense, the objectifications express the causality by which the external world fashions the actual occasion in question. Thus the objectifications of the presented duration represent a recovery by its contem- poraries of a very real efficacy in the determination of M. It is true that the eternal objects which effect this objectification belong to the feeling-tones which M derives from the past. But it is a past which is largely common to M and to the presented duration. Thus by the intermediacy of the past, the presented duration has its efficacy in the production of M. This efficacy does not derogate from the principle of the independence of contemporary occasions. For the contemporary occasions in the presented duration are only efficacious through the feeling-tones of their sources, and not through their own immediate fecling-tones.
Thus in so far as Bergson ascribes the ‘spatialization’ of the world to a distortion introduced by the intellect, he is in error. This spatialization is a real factor in the physical constitution of: every actual occasion belonging to the life history of an enduring physical object. For actual occasions in so-called ‘empty space,’ there is no reason to believe that any duration has been singled out for spatialization; that is to say, that physical perception in the mode of presentational immediacy is negligible for such occasions. The reality of the rest and the motion of enduring physical objects depends on this spatializa-
490 Process and Reality
tion for occasions in their historic routes. The presented duration is the duration in respect to which the enduring object is momentarily at rest. It is that duration which is the strain-locus of that occasion in the life-history of the enduring object.
Measurement
THE identification of the strain-locus with a duration is only an approximation based upon empirical evidence. Their definitions are entirely different. A duration is a complete set of actual occasions, such that all the mem- bers are mutually contemporary one with the other. This property is expressed by the statement that the members enjoy ‘unison of immediacy.’ The completeness consists in the fact that no other actual occasion can be added to the set without loss of this unison of immediacy. Every occasion outside the set is in the past or in the future of some members of the set, and is contemporary with other members of the set. According as an occasion is in the past, or the future, of some members of a dura- tion, the occasion is said to be in the past, or in the future, of that duration.
No occasion can be both in the past and in the future,
of a duration. Thus a duration forms a barrier in the
world between its past and its future. Any route of
occasions, in which adjacent members are contiguous,
and such that it includes members of the past, and mem-
bers of the future, of a duration, must also include one
or more members of that duration. This is the notion
of a duration, which has already been explained (cf. Part
II, Ch. IV, Sects. VIII and IX).
The definition of a strain-locus (cf. previous chapter) depends entirely on the geometrical elements which are the elements of geometric form in the objectification of a nexus including the experient occasion in question. These
492 Process and Reality
elements are (i) a set of points, within the volume of the regional standpoint of the experient occasion, and (11) the set of straight lines defined by all the pairs of these points. The set of points is the ‘seat’ of the strain; the set of straight lines is the set of ‘projectors.’ The com- plete region penetrated by the ‘projectors’ is the strain- locus. A strain-locus is bounded by two ‘flat’ three- dimensional surfaces. When some members of the seat have a special function in the strain-feeling, the projec- tors which join pairs of these points may define a subordi- nate region in the strain-locus; this subordinate region is termed the ‘focal region.’
The strain-loci in the present epoch seem to be con- fined to the contemporaries of their experient occasions. In fact ‘strain-loci’ occur as essential components for per- ception in the mode of presentational immediacy. In this mode of perception there is a unique strain-locus for each such experient. Rest and motion are definable by reference to real strain-loci, and to potential strain-loci. Thus the molecules, forming material bodies for which the science of dynamics is important, may be presumed to have unique strain-loci associated with their prehensions.
This recapitulation of the theories of durations and strain-loci brings out the entire disconnection of their definitions. There is no reason, derivable from these definitions, why there should be any close association between the strain-locus of an experient occasion and any duration including that occasion among its members. It is an empirical fact that mankind invariably conceives the presented world as consisting of such a duration. This is the contemporary world as immediately perceived by the senses. But close association does not necessarily involve unqualified identification. It is permissible, in framing a cosmology to accord with scientific theory, to assume that the associated pair, strain-locus and pre- sented duration, do not involve one and the same exten- sive region. From the point of view of conscious per-
Measurement 493
ception, the divergence may be negligible, though important for scientific theory.
THE notions which have led to the phraseology charac- terizing the ‘projected’ sensa as ‘secondary qualities’ arise out of a fundamental difference between ‘strain-loci’ and their associated ‘presented durations.’ <A strain-locus is entirely determined by the experient in question. It extends beyond that experient indefinitely, although defined by geometrical elements entirely within the extensive region which is the standpoint of the experient. The ‘seat’ of the strain-locus, which is a set of points within this region, is sufficient to effect this definition of the complete strain-locus by the aid of the straight lines termed the ‘projectors.’ These straight lines are nexts whose geometrical relations are forms ingredient in a strain-feeling with these nexiis as data. Presentational immediacy arises from the integration of a strain-feel- ing and a ‘physical purpose,’ so that, by the category of transmutation, the sensum involved in the ‘physical pur- pose’ is projected onto some external focal region defined by projectors.
It is to be noted that this doctrine of presentational immediacy and of the strain-locus entirely depends upon a definition of straight lines in terms of mere extensive- ness. If the definition depends upon the actual physical occasions beyond the experient, the experient should find the actual physical structures of his environment a block, or an assistance, to his ‘projection’ to focal regions beyond them. The projection of sensa in presentational imme- diacy depends entirely upon the state of the brain and upon systematic geometrical relations characterizing the brain. How the brain is excited, whether by visual stimuli through the eye, or by auditory stimuli through the ear, or by the excessive consumption of alcohol, or by hysterical emotion, is completely indifferent; granted the proper excitement of the brain, the experient will per-
494 Process and Reality
ceive some definite contemporary region illustrated by the projected sensa. The indifference of presentational immediacy to contemporary actualities in the environ- ment cannot be exaggerated. It is only by reason of the fortunate dependence of the experient and of these con- temporary actualities on a common past, that presenta- tional immediacy is more than a barren aesthetic display. It does display something, namely, the real extensiveness of the contemporary world. It involves the contempo- rary actualities but only objectifies them as conditioned by extensive relations. It displays a system pervading the world, a world including and transcending the experi- ent. It is a vivid display of systematic real potentiality, inclusive of the experient and reaching beyond it. In so far as straight lines can only be defined in terms of meas- urements, requiring particular actual occasions for their performance, the theory of geometry lacks the requisite disengagement from particular physical fact. The requisite geometrical forms can then only be introduced after examination of the particular actual occasions re- quired for measurement. But the theory of ‘projection,’ explained above, requires that the definition of a com- plete straight line be logically prior to the particular actualities in the extensive environment. This requisite has been supplied by the preceding theory of straight lines (cf. previous chapter). The projectors do depend upon the one experient occasion. But even this depend- ence merely requires that component feelings of that occasion should participate in certain geometric elements, namely, a set of points, and the straight lines defined by them, among their data. Thus, according to this expla- nation, presentational immediacy is the mode in which vivid feelings of contemporary geometrical relations, with especial emphasis on certain ‘focal’ regions, enter into experience.
This doctrine is what common sense always assumes.
When we see a coloured shape, it may be a real man, or a
ghost, or an image behind a mirror, or an hallucination;