78 ON COMPARING COMMODITIES

Many errors appear to have arisen from this
inattention to the real nature of a comparison of
objects at different periods in regard to their
value,

Much indistinctness has also proceeded from
blending the comparison of contemporary commodities
 with that of the same commodity at
different times, particularly when writers have
been speaking of the comparative quantity, or
the comparative value of the labour concerned in
the production of commodities. It is not
always clear to their readers, nor does it seem
to have been clearer to themselves, whether they
intended to compare the same commodity, as
to the producing labour, at separate periods, or
different commodities at the same period.
There appears to me to be considerable confusion
 in this respect in Mr. Ricardo’s first section
 on value; a confusion which is probably
one of the latent causes of the obscurity felt by
many to hang over that section, and which, if I
mistake not, is perceptible in the very sentence
which forms its title.