But the results of most human services may be seen to rest, at least temporarily, in some material form. Effort is put upon a material thing to be used later. The work of the waiter in spreading and arranging the table is not an immediate service, for it is embodied in material form an hour or two before the meal. The service of cook no less than that of gardener and butcher, is put into material form before it comes to the consumer. The woodman fells, cuts up and splits a tree, and piles it at the door, putting his labor into a utility to be consumed months afterward. The old economists used to class labor as productive and unproductive according as it was or was not embodied in material form. The classing of the services of cook, waiter, valet, etc., as unproductive seems, even from the old point of view, to have been inconsistent, and the attempt to distinguish services by any such test is now wholly given up. Whether the service rests in material form for a week, a month, a year, or as often happens, for a much longer period, is not essential. The test of the productiveness of services is not their embodiment in material form, but their appearance as psychic income, their ministry to wants. The most varied kinds of human activity may be unified by this thought in the concept of economic labor. § II. VARIETIES OF TALENTS AND OF ABILITIES IN MEN [Sidenote: Grades of labor are analogous to grades of wealth] 1. _As material things differ in their fitness to gratify wants, so do men differ in their powers of labor._ The fields, hammers, plows, tools, and machinery of different kinds and qualities have been seen to grade off from the best to the poorest. The poorest, discarded or just about to be discarded, are no-rent agents. The utility felt and recognized in the better qualities is expressed in the rents they yield. Recognizing the variety and inequality of human talent, some economists of late speak of the "rent" of ability, meaning that, like land rent, the greater utility (and corresponding reward) of some labor as compared with others, reflects the difference in the quality of agents. But this expression, though often met in contemporary economic writings, is one to be avoided because it tends to blur the essential distinction between human and other agents. Pursuing the same analogy some economists have talked of capitalizing the worker,--expressing in a lump sum the value of the man as the present worth of the series of incomes which he may be expected to earn in his working life. This, also, is to be avoided, for while possibly it is suggestive in studying some problems, it is on the whole a misleading analogy, dimming the distinction between free-workers and owned and exchangeable wealth. [Sidenote: Physical differences among men]