Here a caution is needful. Because nobody can tell what the value of anything is until something else has been put over against it in order to get it and actually received therefor, and because the only possible way to express the value of either is in the terms of the other,--the trowel is worth the wheat and the wheat is worth the trowel,--one must not therefore jump to the conclusion that the value of either is settled for all time or even for any future time. It is only settled for _this_ time. In Economics as in Christianity, Now is the accepted time. There is nothing fixed in Values, and never can be from the nature of the case, because Desires are personal to individuals, and Efforts fluctuate with times and persons, and Estimates that wait on these vary from necessity, and the Renderings of to-day may not be the chosen renderings of other persons in the same articles to-morrow. Value is not a quality at all, still less is it a permanent quality, of anything; it is a relation established between two things when these are in the hands of two given persons; but now when these are in the hands of two different persons, whose views are pretty sure to differ from the former, and a new relation is sought to be established between these in the old way of Estimates, is it strange that a new balance is struck, and Value is expressed in quite different terms? One of the chief charms of Political Economy is the open secret, that it deals not with rigidities and inflexible qualities and mathematical quantities and the unchanging laws of matter, but with the billowy play of desires and estimates and purposes and satisfactions, all of which are mental states, and all of which are subject in the general to ascertainable laws, though laws of a quite different kind from those of Mechanics. Values come and they go. Within certain limits and under certain conditions they may be anticipated and even predicted, but never with the precision of an eclipse or the result of a known chemical combination. There is a useful and fascinating Science of Value, as we shall see indubitably by and by in the present chapter; but it is a science that deals primarily with _persons_ and only secondarily with _things_, with mind and not with matter, with the general undulations of the sea and not with the crests of the waves. And all this is so, because Values are relative, because the announcements in the market-place to-day may stand listed differently to-morrow and very differently next year, and because old values may disappear altogether and many new ones come in, all in accordance with the incessant changes in the wants and labors and fashions and projects of men.