The proposition must be understood as applying to the gratification resulting from each added portion of the sensation. There is a maximum point in the gratification afforded by any nerve-stimulus. A man coming in from the winter's storm and holding out his hands before the fire, feels an intense pleasure in the grateful warmth; a few moments later, the same heat becomes unpleasant. In winter we wish for a moderation of the temperature; on the sultry days of summer, we think of a cool breeze as the most to be desired of all things. Whether the temperature rises or falls, there is a point beyond which the change is no longer an addition to, but a subtraction from, pleasure. A man, however hungry at first, may be made miserable if forced to eat beyond his capacity. Each added portion of the good consumed contributes to the gratification up to a certain point. The sum of these pleasurable sensations may be called the total gratification, which finally reaches satisfaction or fullness. Then begins what may be called in algebraic phrase a "negative gratification" which, if it becomes large enough, will make the total gratification a negative quantity. Each added portion, dose or increment beyond a certain point reduces thus the welfare of the user. One may have too much of a good thing. [Sidenote: The marginal utility] 4. _Marginal utility is the gratification afforded by the added portion of the good._ The marginal dose, increment, or portion is that which may be logically considered as coming last in the case of any good or group of goods divisible into small parts. In considering the strict theory of the case, in order to get at the principle involved, the doses may be spoken of as infinitesimally small. The marginal utility expresses the importance that men attach to one unit of this kind of goods under the particular circumstances at the moment existing, and not under certain conceivable conditions which do not in fact exist or need to be taken into account by the persons affected. The marginal unit of a homogeneous supply cannot be considered to have a greater utility than any other unit at the moment, and therefore the product of the marginal utility by the number of units, gives the total measure of importance of the supply then and there, and this is the value.