The actual utility of goods at a specific time and place depends on the nature of the wants that can then and there be satisfied, as well as upon the inherent characteristics of the goods themselves. Food, for instance, has a high utility if it is available when and where it is needed. It does not follow, however, that an infinite amount of food at that time and place would have infinite utility. If Crusoe picks and eats a banana, the fruit contributes toward relieving his hunger, a very important want, and it also satisfies his desire for a tasty food, another want distinct from mere nutrition. A second banana is not quite the equal of the first, as the sharp edge has been taken off the hunger sensation, and the taste satisfaction probably lacks something of being the equal of that gained from the original unit. By the time he reaches the fifth or sixth banana, the ability of another one to satisfy either hunger or taste at this time has sunk to a low level, and if he keeps up the process he soon arrives at a point where bananas have no further utility to him at the moment. This situation, we find, is not a peculiarity of bananas, but is characteristic of utilities in general. After the point of maximum utility (often the first unit) is passed, the utility of each successive additional unit becomes less and less until it finally reaches the vicinity of zero. This is called the principle of diminishing utility, and it is one manifestation of the general principle of diminishing returns, a mathematically based relation of very wide applicability. For many economic processes the utility of the last unit of a kind, the marginal unit, has a particular significance. Of course, any one of the groups could be the marginal unit. In the case of the bananas, no specific one can be singled out, prior to being selected for eating, as having more utility than another, but this is simply because we cannot tell in advance which will be selected first . We can, however, say definitely that the first banana picked will have the maximum utility, and the last one will have the least utility. As soon as the selection is made, the utility is determined. The utility of the last, or marginal, unit is the marginal utility of the total supply of bananas.