230 ON THE CAUSES

these commodities, which are left in every way
perfectly free to competition, the practical truth
inculcated by Mr. Ricardo is this, that if the
quantity of labour necessary for the production
of a commodity is increased or decreased, it
rises or falls in value in relation to other commodities,
 of which the quantity of producing
labour is not altered. This, however, is a truth
not dependent on the quantity of labour being
the sole cause of value, but on its being one of
the causes. The same is true of every other
cause of value. Any effect is necessarily increased
 if we increase any of its causes.
Mr. Ricardo, indeed, explicitly allows the
influence of other causes, such as time, differences
 in the proportion of fixed and circulating
capital, and inequalities in the durability of
capital, by which he admits the value of commodities
 is liable to be affected. Notwithstanding
 these modifications, however, his followers
continue to lay down the position of quantity
of labour being the sole cause of value in the
most precise and positive terms; not that they