Routledge History of Philosophy Volume IV

GASSENDI AND HOBBES 239
(De corp. ch. 25, ii, E I 390)
‘Press’ and ‘pressure’ are terms from the theory of pure mechanics. Hobbes
defines them in Part Three of De Corpore. One body presses another when ‘with
its endeavour’ the first body displaces the other or displaces part of the other (De
corp. ch. 15, ii, E I 211). In the case of sensation, the pressure on the outermost
part of the sense organ is exened either by the body sensed, what Hobbes calls
‘the object of sense’, or by some part of the medium, like air, which is itself set
in motion by the object of sense. The pressure on the outermost part of the organ
of sense displaces the nearest internal parts, which in turn press the next
adjoining, which in turn press the next. Sensation does not result simply from
this communication of pressure, but from the resistance of pressed to pressing
bodies. Each pressure inwards is met with resistance outwards by the parts of the
sense organ, so that there is a chain of reactions to a chain of pressures in the
parts of the organ. From the last of this chain of reactions and its effect on the
brain ‘a phantasm or idea hath its being’ (ch. 25, ii, E I 391). Only the strongest
of the endeavours outward from the innermost parts of the sense organ
constitutes a sensory reaction, and there can only be one sensory reaction at a time.
Moreover, a given sensory reaction at a time can be experience of no more than
one object at a time (De corp. ch. 25, v, E I 395), if the various sense organs are
applied at a single time to a single object. So sense experience is an orderly
succession of images of discrete things.
This much of the theory of sense is supposed to explain more than the
existence of phantasms and their occurring in orderly sequences: it explains also
some features of their content. For example, since a phantasm or idea results
from the last of a chain of reactions outwards in the parts of the sense organ, to
have a phantasm of a thing is to have an experience as of something outside the
organ of sense (ibid.). Again, the theory as so far sketched makes some sense of
the fact that ‘things when they are not the same seem not to be the same but
changed’ (cf. De corp. ch. 6, vi, E I 72). Hobbes gives the example of things that
appear to sight to be different sizes at different times. This is the effect of
variations in the angle at which motion from the innermost part of the organ of
sight is propagated outwards (De corp. ch. 25, xi, E I 405). Another phenomenon
is variation in the number of stars visible in the heavens. This is the effect not of
generation or destruction of stars, but of the state of the medium through which
the motion of the stars is propagated. Cold air facilitates, and hot air hinders,
stellar action on the eyes; so more stars appear on cold, calm nights, than on
warm, windy ones (cf. De corp. ch. 25, xi, E I 406).
Hobbes’s theory of sense is an account not only of the objects and causes of
phantasms but also of the cognitive operations performed with them. To be
endowed with sense, Hobbes believes, is not merely to be the momentary site of
phantasms; it is to be able to recall ideas to mind, and to be able to compare and
distinguish them. Indeed, judgement, which is the capacity to keep track of
differences between objects presented to the senses (De corp. ch. 25, viii, E I