[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