140 ON THE MEASURE OF VALUE
value, Mr. Malthus maintains that the value of
labour is invariable.

The discussions in which we have already
been engaged, furnish a variety of methods in
which the errors of this doctrine may be ex-
posed.

It has been shown, for example, that the value
of labour, like that of any other exchangeable
article, is denoted by the quantity of some
other commodity for which a definite portion of
it will exchange, and must rise or fall as that
quantity becomes greater or smaller, these
phrases being in truth only different expressions
of the same event. Hence, unless labour always
exchanges for the same quantity of other things,
its value cannot be invariable ; and consequently,
the very supposition of its being at one and the
same time invariable, and capable of measur-
ing the variations of other commodities, in-
volves a direct contradiction.

It has also been shown, that to term any
thing immutable in value, amidst the fluctua-
tions of other things, implies that its value at
one time may be compared with its value at