Essays Towards a Theory of Knowledge | Page 4

seem to follow that those who hold Sensation
to be the only source of our Knowledge must be obliged to affirm the
possibility of sensations of Space. Mach indeed claims to distinguish
physiological Space, geometrical Space, visual Space, tactual Space as
all different and yet apparently harmoniously blended in our
Experience. He is, however, sadly wanting in clearness of statement.
He never tells us when and where exactly we do have a sensation of
Space. In truth he never gets behind the postulate of an all-enveloping
tridimensional world; so that he throughout assumes Space as a datum,
and his inquiry is an effort to rediscover Space where he has already
placed it.
Let us, however, consider for a moment what can be meant by a
sensation of Space. Does it not look very like a contradiction in terms?
Pure Space, if it means anything, means absolute material emptiness
and vacuity. How, then, by any possibility can it give rise to a sensation?
What sensory organ can it be conceived as affecting? How and in what
way can it be felt?
The truth is the idea of Space is essentially negative. It represents
absence of physical obstruction of every kind. No doubt, we may
describe it positively as a possibility of free movement, and such a
description is at once true and important. Yet even it involves a

negative. The term "free" is in reality, though not in form, a negative
term and means "unconstrained." And the reason why such a term is
necessarily negative is to be found in the fact that a state of dynamic
constraint is the essential condition under which we enter upon our
organic existence. Freedom is a negation of the Actual. Absolute
freedom is a condition only theoretically possible, and is essentially the
negation of the state of restraint in which our life is maintained.
But the definition last quoted is nevertheless valuable because it clearly
shows what really is the origin of the idea of Space. It proves that the
idea of Space is a representation of one condition of our Activity. It is
because the primary work of Thought is to represent the forms of our
dynamic Activity that we find the idea of Space so necessary and
fundamental.
But it will perhaps be argued that our ordinary sensations carry with
them a spatial meaning and implication, and that indirectly, therefore,
our sensations do supply us with the idea of Space. It will readily be
agreed that if this is so of any sensations it is pre-eminently true of the
sensations of vision and touch. Indeed, it will perhaps not be disputed
that the ordinary vident man derives from the sensations of vision his
most common spatial conceptions. We propose, therefore, to inquire
very briefly how the character of spatial extension becomes associated
with the data of Vision.
The objects of Vision appear to be displayed before us in immense
multitude, each distinct from its adjacent neighbour, yet all inter-related
as parts of one single whole--the presentation thus constituting what is
called Extensity.
This is the most commonly employed meaning of the term spatial. Yet
it is evidently in its origin rather temporal than spatial. In ordinary
movement we encounter by touch various obstacles, but only a very
few of these impress us at any one moment of time. On the contrary,
they succeed one after the other. To the blind, therefore, as Platner long
ago remarked: Time serves instead of Space. In Vision, on the other
hand, a large number, which it would take a very long time to
encounter in touch, are presented simultaneously. In this there is an

immense practical advantage, the result being that we come habitually
to direct our every action by reference to the data of Sight. Now it is
because these data--so simultaneously presented--are employed by us
as the guides of action that their presentation acquires the character
which we denominate Extensity. The simultaneous occurrence of a
large number of Sounds does not seem to us to present such a character.
But let us suppose that all the objects which constitute obstacles to our
Activity emitted Sounds by which they were recognised; it is not
doubtful that these would then come to be employed by us as the
guides of our Activity and would acquire in our minds the character of
Extensity. They would arrange themselves in a cotemporaneous,
extensive, or spatial relation to one another just as the objects of Vision
do at present.
It is only, therefore, when we come to employ the simultaneous
presentation of Vision as the instrument of our Activity and the guide
of Action that it acquires the character commonly called extensive.
Successive visual sensations convey no extensive suggestion.
It is important to realise the nature of this peculiar feature in the