[76 DIFFERENCE BETWEEN
It is certainly true, that, provided quantity of
labour were the sole cause of value, we should
always be able to deduce the value of two comi-
modities from a knowledge of the quantities of
labour which they respectively required to pro-
duce them ; and in this sense, quantity of la-
bour would be at once the cause and the mea-
sure of value. But even under these circum-
stances, an author would not be justified in an
indiscriminate use of the terms; nor could he
fall into such an error, had he a distinct ap-
prehension of the difference between the two
ideas.
[t would by no means follow, however, from
quantity of labour being the cause of value,
that it would be of any service as a measure.
On this point we may adopt the language of
the author of the Dialogues: ‘ If it had been
proposed as a measure of value, we might
justly demand that it should be ready and easy
of application ; but it is manifestly not so; for
the quantity of labour employed in producing
A, ¢ could not in many cases’ (as Mr. Malthus