We have seen, however, that even in the case of metallic currency, the immediate agency in determining its value is its quantity. If the quantity, instead of depending on the ordinary mercantile motives of profit and loss, could be arbitrarily fixed by authority, the value would depend on the fiat of that authority, not on cost of production. The quantity of a paper currency not convertible into the metals at the option of the holder _can_ be arbitrarily fixed, especially if the issuer is the sovereign power of the state. The value, therefore, of such a currency is entirely arbitrary. The value of paper money is, of course, primarily and mainly dependent on the quantity issued. The general level of value depends on the _quantity_; but we also find that deviations from this general level, in the direction of further depreciation than could be due to quantity alone, is caused by any event which shakes the confidence of any one that he may get the existing value for his paper. The “convention” by which real value (the essential idea of money) was associated with this paper in the minds of all is thereby broken. _Fiat_ money—that is, a piece of paper, not containing a promise to pay a dollar, but a simple declaration that this is a dollar—therefore, separates the paper from any connection with value. And yet we see that _fiat_ money has some, although a fluctuating, value at certain times: if the State receives it for taxes, if it is a legal acquittal of obligations, then, to that extent, a certain quantity of it is given a value equal to the wealth represented by the taxes, or the debts. Jevons remarks on this point(247) that, if “the quantity of notes issued was kept within such moderate limits that any one wishing to realize the metallic value of the notes could find some one wanting to pay taxes, and therefore willing to give coin for notes,” stability of value might be secured. If there is more in circulation than performs these functions, it will depreciate in the proportion of the _quantity_ to the extent of the uses assigned to it; so that the relation of quantity to uses is the only thing which can give value to _fiat_ money, but beyond a certain point in the issues other forces than mere quantity begin to affect the value. Although the paper is not even a promise to pay value, the form of expression on its face, or the term used as its designation, generally tends, under the force of convention and habit, to give a popular value to paper.