DEMAND AND VALUE 23

Accepting marginal demand price as an index of
marginal utility, this principle is often referred to as the
principle of diminishing utility. As above stated, it is of
extremely general applicability. The exceptions may, however,
 be deemed to require at least a passing reference.
We shall refer to three different classes of exception.
The first is not, in reality, an exception as the principle
has been enunciated, and not a universal exception however
the principle be regarded. It is the case, not of desire for
one particular commodity, but for wealth in general, and for
money as the means of procuring all other commodities,
With some persons, and in some stages of the accumulation
of individual wealth, it is observed to be the case that the
appetite grows by what it feeds on. In a vast majority of
cases, however, even if we regard wealth in general instead
of some one particular commodity, it may be laid down
that the more urgent wants are first satisfied, and that,
therefore, additions to wealth could only be applied to the
satisfaction of wants less imperious than those already
satisfied. In so far as this is true, the marginal utility of
wealth, and not merely of any one form of wealth, av be
said to decrease as its supply increases.
The second case may be illustrated by the victim of
alcoholism, whose craving for more stimulant often grows as
he gratifies it.
The third case has as type the collector, whose desire
to acquire any further extant specimens of things of which
his collection already possesses examples, may become by
50 much the more intense as his collection approaches
exhaustiveness. This case, again, is quite usually not
strictly an exception to the principle laid down, as the
desired specimens are often not identical copies of one
article, but examples of a class. It may be admitted,
however, as an exception to the general rule,
There appear, further, to be some cases where, until the
supply has reached a, more or less definite, considerable
amount, desire for more grows with the supply, but a relative
satiety is attained at last, and further supplies, even if affording
 additional satisfaction, afford it in diminishing degree.