OF VALUE. 
215 
proposed, not only as the cause but the measure 
of value, that which is itself unascertainable. 
There are only two possible methods of com- 
paring one quantity of labour with another; 
one is to compare them by the time expended, 
the other by the result produced. The former 
is applicable to all kinds of [abour; the latter 
can be used only in comparing labour bestowed 
on similar articles. If therefore, in estimating 
two different sorts of work, the time spent will 
not determine the proportion between the 
quantities of labour, it must remain undeter- 
mined and undeterminable. 
2. We are furnished with cases of the second 
kind (namely, those in which two commodities, 
once equal in value, have become unequal in 
value without any change in the quantity of la- 
bour respectively employed in aech) by Mr. Ri- 
cardo himself. 
Take any two commodities of equal value, 
a and B, one produced by fixed capital and the 
other by labour, without the intervention of ma- 
chinery ; and suppose, that without any change