_How Primitive Man tests Value._--It is a mistake to suppose that what is essential in value depends on the existence of an actual market in which things are exchanged for each other. In a market, it is true, values are established and their amounts are expressed in ways that cannot be adopted in primitive life. When we buy a thing, we help to fix the value of it and of other things which are like it. The mere ratios in which things exchange for each other in a market are, however, by no means the essence of value itself. That is something deeper and is one of the universal phenomena of wealth. Value, as we have said, is the measure of the effective utility of things, a kind of measure that every one is frequently compelled to employ, whether he is making goods for himself or buying them from others. A producer who has the option of making different things for himself needs to know what variety of goods can be increased in supply with the greatest advantage to himself as a consumer. Adding to the supply of any one of them is getting a "final" or "marginal" unit of consumers' wealth. It is something that is needed less than the things that were already on hand. Without making such a comparison of the importance of marginal units of different commodities he cannot use his resources in the way that will do him the most good.[3] [3] [Illustration] The terms _marginal_ and _final_ mean essentially the same thing, but the modes of conceiving it differ. When utilities are thought of as supplied one after another, the last is the least important. We may represent a man's enlarging gratifications, not by such a mere series of quantitative increments, but by an enlarging area. We may draw a series of concentric circles, beginning with the smallest, and let this central area inclose the most necessary forms of consumers' wealth. When we draw a second and larger circle, we inclose between it and the first one a zone which includes those forms which come next in importance. By continuing to draw circles we reach an outermost one which bounds a zone in which are included the least important of the consumer's acquisitions. These are the things which he gets with his costliest increment of labor, and the things which lie beyond the circle last drawn would not pay for the sacrifice which acquiring them would cost. In the accompanying figure the fifth zone includes these "marginal" forms of wealth.