An essay on the foundations of geometryRussell, Bertrand
Philosophy
An essay on the foundations of geometry
Russell, Bertrand
Geometry -- Foundations
The second possibility also, Lotze thinks, is not that of
Metageometry, but in truth it comes nearer to it than any of the
other possibilities discussed. If a non-Euclidean were at the same
time a believer in the subjectivity of space, he would have to be
an adherent of this view. Let us see more precisely what the view
is. In Book II., Chapter I., Lotze has accepted the argument of the
Transcendental Aesthetic, but rejected that of the mathematical
antinomies: he has decided that space is, as Kant believed,
subjective, but possesses nevertheless, what Kant denied it, an
objective counterpart. The relation of presented space to its
objective counterpart, as conceived by Lotze, is rather hard to
understand. It seems scarcely to resemble the relation of sensation
to its object--_e.g._ of light to ether-vibrations--for if it did,
space would not be in any peculiar sense subjective. It seems rather
to resemble the relation of a perceived bodily motion to the state
of mind of the person willing the motion. However this may be, the
objective counterpart of space is supposed to consist of certain
immediate interactions of monads, who experience the interactions
as modifications of their internal states. Such interactions, it
is plain, do not form the subject-matter of Geometry, which deals
only with our resulting perceptions of spatial figures. Now if
Lotze's construction of space be correct, there seems certainly
no reason why these resulting perceptions should not, for one and
the same interaction between monads, be very different in beings
differently constituted from ourselves. But if they were different,
says Lotze, they would have to be utterly different--as different,
for example, as the interval between two notes is from a straight
line. The possibility is, therefore, in his opinion, one about which
we can know nothing, and one which must remain always a mere empty
idea. This seems to me to go too far: for whatever the objective
counterpart may be, any argument which gives us information about
it must, when reversed, give us information about any possible form
of intuition in which this counterpart is presented. The argument
which Lotze has used in his former chapter, for example, deducing,
from the relativity of position, the merely relational nature of
the objective counterpart, allows us, conversely, to infer, from
this relational nature, the complete relativity of position in any
possible space-intuition--unless, indeed, it bore a wholly deceitful
relation to those interactions of monads which form its objective
counterpart. But the complete relativity of position, as I shall
endeavour to establish in Chapter III., suffices to prove that our
Geometry must be Euclidean, elliptic, spherical or pseudo-spherical.
We have, therefore, it would seem, very considerable knowledge,
on Lotze's theory of space, of the manner in which what appears
to us as space _must_ appear to any beings with our laws of
thought.
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