2. _Demand is the social aspect of the individual man's comparison of utilities._ It is the expression of the man's wish to substitute some of his goods for some one else's goods in order to get a higher satisfaction. This comparison is often made between two goods owned in different quantities. When men are constantly comparing things in their own possession, it is a short step to compare their goods with their neighbor's. Demand for consumption goods is thus the manifestation of the man's desire to redistribute his enjoyments. In demand for goods men virtually say: "Part of what I have I am ready to give for part of what you have." The strength of their desire is expressed by the amount of their offer. When he makes this comparison and this offer, man enters into a social, economic relation with his fellows. [Sidenote: The limit of the exchanger's demand] 3. _The law of individual demand is: The trader will reduce his stock of a particular good to the point where its marginal utility equals that of the alternative goods._ The greater the divergence in his estimates of the marginal utilities of two goods, the more ready is he to trade the lower utility for the higher one. Exchange is but the effort to adjust goods to wants in the best way. The less useful (marginally viewed) is traded for the more useful. The greater the difference, in the one trader's judgment, between the marginal utilities of the two goods, the greater is the maladjustment, and the greater, therefore, is the motive to seek readjustment by means of exchange. As the quantity of the good parted with declines, its marginal utility increases; and as more of the other good is acquired, its marginal utility declines. The marginal utility of the two exchangeable units must come to equilibrium in the individual's judgment. At this point demand ceases, not because an additional unit of the one good could afford no gratification, but because it would afford less gratification than the other good in which demand must be expressed to be effectual. [Sidenote: The Demand curve] 4. _Demand thus varies at different ratios of exchange between goods, and may be expressed graphically by a demand curve._ This would show for any one man the decline of the marginal utility of each added portion of a good, and these individual demand curves may be united into a demand curve for a group of men. The demand curve expresses graphically what a man would be willing to pay at each particular stage in the increase of goods. We have here come to the very threshold of the subject of markets and exchange. [Sidenote: Elasticity of demand]