Examination of a number of particular cases will fully elucidate the principles here set forth, and I do not wish to shirk this important task, even though I know that I shall appear tiresome to some readers. Following in the path of Adam Smith, I will risk some tediousness to gain clarity of exposition.
To begin with the simplest case, suppose that an isolated economizing individual inhabits a rocky island in the sea, that he finds only a single spring on the island, and that he is exclusively dependent upon it for satisfaction of his need for fresh water. Assume that this isolated individual needs: (a) one unit of water
daily for the maintenance of his life, (b) nineteen units for the animals whose milk and meat provide him with the most necessary means of subsistence, (c) forty units, partly so that he may consume the full quantity necessary to the maintenance not only of his life but also his health; partly, to the extent necessary for the continuance of his health and general well-being, to clean his body, his clothes, and his implements; and partly for the support of some additional animals whose milk and meat he finds needful, and finally (d) forty additional units of water daily, partly for his flower garden, and partly for some animals, which he keeps, not for the maintenance of his life and health, but simply for the purpose of a more varied diet, or for mere companionship. Assume too that he does not know how to employ more than this total of one hundred units of water.
As long as the spring provides water so copiously that he can not only satisfy all his needs for water but let several thousand pails flow into the sea every day, and thus as long as the satisfaction of none of his needs depends upon whether he has one unit more or one unit less (e.g., one pail full) at his disposal, a unit of
water will, as we have seen, have neither economic character nor value to him, and thus there can be no question of the magnitude of its value. But if some natural event should now suddenly cause the spring to become partially exhausted, and if our island dweller should, as a result, have only 90 units of water at his disposal while he continues to require 100 units for the full satisfaction of his needs, it is clear that some satisfaction would then be dependent on the availability of each portion of the whole supply of water, and hence that each particular unit of water would attain that significance for him that we call value.
If we now, however, ask which of his satisfactions is, in this case, dependent on a given portion of the 90 units of water available to him, on 10 units for instance, our question takes the following form: which satisfactions of our isolated individual would not be attained if he did not have this given portion of the supply at his disposal-that is, if he should have only 80 instead of go units?
Nothing is more certain than that our economizing individual would continue, even if he had only 80 units of water available daily, to consume the quantity necessary for the preservation of his life, and as much more as will maintain as many animals as are indispensable for keeping him alive. Since these purposes require
only 20 units of water daily, he would apply the remaining 60 units first to the satisfaction of all the needs on which his health and his continuing general well-being depend. Since for this purpose he requires a total of only 40 pails of water daily, he would have 20 units left, which could be employed for purposes of mere enjoyment. The last 20 units could thus maintain either his flower garden or the animals he owns purely for pleasure. He would certainly choose, from the two satisfactions, the one appearing to him to be the more important, and would neglect the less important one.
When our Crusoe has 90 units of water available to him daily, the question whether he will continue to have this quantity or 10 units less at his disposal is, for him, equivalent to the question whether or not he will be in a position to continue to satisfy the least important needs that are being satisfied with 10 units of water daily. As long, therefore, as a total quantity of go units continues at his disposal, 10 units of water will have only the importance of these least important satisfactions-that is, only the importance of relatively insignificant enjoyments.
Taken From : PRINCIPLES OF ECONOMICS
