3. _Labor and material wealth are complementary and indispensable to each other in most of their uses._ The discussion of material wealth and its value apart from the subject of labor, of the problem of rent and interest apart from that of wages, does not imply that this material wealth would have the same value in real life if labor were absent. As one field affects the value of another field, and one good, by substitution, the value of another good, so does labor affect material wealth. Some material wealth can be used apart from labor, but most of it must be used in combination with some labor. Rent, therefore, is not determined in concrete cases apart from men and their services. It is allowable, however, in abstract analysis, to simplify the question by leaving out a difficult complication, and thus to set forth more clearly the logical bearing and effect of a certain factor. [Sidenote: Certain shares of the product are logically attributed to each] Each of two kinds of agents used together affects the utility of the other, and the value of the product. If neither can be credited with the whole value, how is any distribution to be made between them? It is not possible to measure their technical services in the product, but it usually is possible to gage their marginal utility under particular conditions. Flour, water, and labor are needed to make biscuits; but water being a free agent, does not enter into the combination with any marginal utility. A match also is almost indispensable to start the fire (and who has not seen the time when he would give far more for a match than for a bucket of coal), but as things usually are, the match is credited with a value of a very small fraction of a cent. Again, how is to be measured the economic service of the tree and of the labor needed for gathering its fruits? There is here suggested the superficial aspect of what is known as the problem of complementary values. Where two or more things are indispensable to a product, how much shall be credited to each? [Sidenote: Labor gratifies directly and indirectly] 4. _Human service has the same general relation to wants that material goods have, affording gratification either directly or indirectly._ It is axiomatic that to be "economic goods" human efforts like material goods must afford utilities whose importance is felt. Many services give pleasure directly and are immediately consumed. A tropical potentate has an attendant to fan him, and another to carry an umbrella; a humble citizen is shaved, doctored, sung to, and played for. The gratification in such cases is directly produced in personal comfort, in the consciousness of heightened beauty, in the feeling of self-esteem. Value is thus created and consumed immediately, taking no material form apart from the consumer. [Sidenote: Labor embodied for a time in material form]