"Value is a relative term. The value of a thing means the quantity of some other thing, or of things in general, which it exchanges for. The values of all things can never, therefore, rise or fall simultaneously. There is no such thing as a general rise or a general fall of values. Every rise of value supposes a fall, and every fall a rise." Again, he says:-- "Things which are exchanged for one another can no more all fall, or all rise, than a dozen runners can each outstrip all the rest, or a hundred trees all overtop one another." Prof. S. N. Patten says, in "Dynamic Economics," p. 64: "Objective values, however, are never a sum, but only a relation between subjective values. There can never be high or low objective values of commodities as a whole. It is therefore impossible to add to or subtract from them." This latter quotation, as well as the preceding one from von Böhm-Bawerk,--both exponents of the marginal utility theory,--may help to correct a quite prevalent impression that this later theory does not distinguish between the two conceptions of value, and that because the sum of subjective values may increase, the sum of objective or exchange values can increase also. _Supply and Demand._ All economists recognize the fact that the immediate determiner of value is the relation between supply and demand. These terms in their economic sense mean something more than mere desire and mere quantity. _Supply_ means the amount offered in exchange, and _demand_ means not only a desire, but a desire coupled with the ability and willingness to give other commodities in exchange for the one wanted. In this sense the terms are strictly correlative. The supply of a commodity (that is, the amount offered) may be considered as equivalent to a demand for some other commodity, or for commodities in general. We may say, then, that the value of any commodity is determined by the ratio that the demand for that commodity bears to its supply; or by the ratio that the demand for that commodity bears to the demand for some other commodity,--or commodities in general, when the term _value_ is used in a general sense and not with reference to some other specified thing only. (The objection that has been made by some writers that a ratio could not logically exist between a desire [demand] and a quantity [supply], does not apply to these terms in their economic sense; for, as above stated, they are something more than a mere desire and a mere quantity, and the expression is translatable into the other expression, "ratio between the demand for one commodity and the demand for others in general.")