A MEASURE AND A CAUSE OF VALUE. 177 
truly objects) © be ascertained without con- 
siderable difficulty :’ in most cases, indeed, it 
could not be ascertained at all. A measure of 
value, however, which cannot be practically 
applied, is worthless*.” 
It was probably some obscure and undefined 
impression of this truth, which, when Mr. Ri- 
cardo deliberately set himself to treat on the 
subject of a measure of value, influenced him 
to speak, not of labour itself in that capacity, 
but of a commodity produced by an invariable 
quantity of labour. If the quantity of pro- 
ducing labour really determines the value of 
commodities, it seems on a first view useless to 
require for a measure an object of which the 
producing labour is invariable, when we may 
have recourse to the labour itself. But Mr. Ri- 
cardo probably perceived, that a knowledge of 
the quantity of producing labour in objects 
would be in most cases difficult of attainment, 
and therefore betook himself to the considera~ 
x 
London Magazine for May, 1824, page 559.