successful, it promises to some need or desire. Thus 'thought' is
everywhere inspired by 'will.' It is an _instrument_, the most potent
man has found, whereby he brings about a harmony with his environment.
This harmony is always something of a compromise. We postulate
conformity between Nature and one of our ideals. We usually desire more
than we can get, but insist on all that Nature can concede.

Causation serves as a good example. Experience as it first comes to us
is a mere flood of happenings, with no distinction between causal and
casual sequences. Clearly our whole ability to control our life, or even
to continue it, demands that we should _predict_ what happens, and guide
our actions accordingly. We therefore postulate a right to _dissect_
the flux, to fit together selected series without reference to the
rest. Thus, a systematic network of natural 'laws' is slowly knit
together, and chaos visibly transforms itself into scientific order. The
postulation of 'causes' is verified by its success. Moreover, it is to
be noted that to this postulate there is no alternative. A belief that
all events are casual would be scientifically worthless. So is a
doctrine (still popular among philosophers) that the only true 'cause'
is the total universe at one moment, the only true 'effect,' the whole
of reality at the next. For that is merely to reinstate the given chaos
science tried to analyse, and to forbid us to make selections from it.
It would make prediction wholly vain, and entangle truth in a totality
of things which is unique at every instant, and never can recur.

The principles of mathematics are as clearly postulates. In Euclidean
geometry we assume definitions of 'points,' 'lines,' 'surfaces,' etc.,
which are never found in nature, but form the most convenient
abstractions for measuring things. Both 'space' and 'time,' as defined
for mathematical purposes, are ideal constructions drawn from empirical