however, that this alteration in the supply of wool was a matter not
only of quantity but of quality, while it takes nothing from the
substance of the preceding argument, makes it difficult to draw a
clear moral, bearing on the present issue, from this incursion into
history.


§4. _The Importance of being Unimportant_. The above contrast between
cases in which variation is possible, and those in which it is not
possible, is reproduced with a heightened significance when we turn
back to joint demand. The cases are perhaps less common in which it is
_impossible_ to alter the proportions in which different commodities
are jointly demanded, but there are many cases in which it is not
nearly worth while to do so (and this amounts to very much the same
thing). Cases of this sort are especially likely to occur when we are
dealing with a commodity which accounts for only a tiny fraction of
the costs of the industry which is its chief consumer. Sewing cotton,
for example, is jointly demanded, with many other things, by the
tailoring and other clothing trades; but the money which these trades
spend on sewing cotton is so small a part of their total expenditure,
that no ordinary variation in its price is likely to make it worth
while to study the ways and means of using it in smaller
quantities. When sewing cotton is bought by the domestic consumer,
considerations which are fundamentally the same, though somewhat
different in form, point to a similar conclusion. It is thus very
difficult to assign to sewing cotton a specific marginal utility. This
difficulty is of great importance in connection with the possibilities
of monopolistic exploitation. For it means that the demand blade of
the scissors upon which we rely to cut off excrescences of price is
blunted, and if accordingly the producers constitute a strong enough