【正文】 tific program. There is still a need for thoroughgoing and critical parison and contrast of theoretical assumptions with the conditions of real life and of theoretical conclusions with concrete facts. The makers and users of economic analysis have in general still to be made to see that deductions from theory are necessary, not because literally true— that in the strict sense they are useful because not literally true— but only if they bear a certain relation to literal truth and if all who work with them constantly bear in mind what that relation is. It must be admitted that even the pure theorists have not generally been assiduous in emphasizing the practical significance of their work and its relation to the outside body of the science。 it is imperative that the contrast between these simplified assumptions and the plex facts of life be made as conspicuous and as familiar as has been done in mechanics. The present essay is an attempt in the direction indicated above. We shall endeavor to search out and placard the unrealities of the postulates of theoretical economics, not for the purpose of discrediting the doctrine, but with a view to making clear its theoretical limitations. There are several reasons why the approximate character of theoretical economic laws and their inapplicability without empirical correction to real situations should be especially emphasized as pared, for instance, with those of mechanics. The first reason is historical and has already been indicated. The limitations of the results have not always been clear, and theorists themselves as well as writers in practical economics and statecraft have carelessly used them without regard for the corrections necessary to make them fit concrete facts. Policies must fail, and fail disastrously, which are based on perpetual motion reasoning without the recognition that it is such. In the second place, the allowances and corrections necessary in the case of theoretical economics are vastly greater than in the case of mechanics, and the importance of not losing sight of them is correspondingly accentuated. The general principles do not bring us so close to reality。 but it is a very fundamental section, in a sense the first of all, the foundation and prerequisite of those that follow. And this also may very well hold good of a body of pure theory in economics。 its ideal is analytic treatment, and analysis and abstraction are virtually synonyms. We have given us the task of reducing to order a plex mass of interrelated changes, which is to say, of analyzing them into uniformities of sequence or behavior, called laws, and the isolation of the different elementary sequences for separate study. Sometimes the various elementary constituents of our plex phenomenon are met with in nature in isolation plete or partial, and sometimes artificial experiments can be devised to present them either alone or with attendant conditions subject to control. The latter is, of course, the characteristic procedure of physical science. Its application to the study of industrial society is, however, generally impracticable. Here we must monly search for manifestations of the various factors in our plex, under varying associations, or rely upon intuitive knowledge of general principles and follow through the workings of individual chains of sequence by logical processes. The application of the analytic method in any class of problems is always very inplete. It is never possible to deal in this way with a very large proportion, numerically speaking, of the vast plexity of factors entering into a normal real situation such as we must cope with in practical life. The value of the method depends on the fact that in large groups of problem situations certain elements are mon and are not merely present in each single case, but in addition are both few in number and important enough largely to dominate the situations. The laws of these few elements, therefore, enable us to reach an approximation to the law of the situation as a whole. They give us statements of what tends to hold true or would hold true under ideal conditions, meaning merely in a situation where the numerous and variable but less important other things which our laws do not take into account were entirely absent. Thus, in physics, the model and archetype of an exact science of nature, a relatively small and workable number of laws or principles tell us what would happen if simplified conditions be assumed and all disturbing factors eliminated. The simplified conditions include specifications as to dimensions, mass, shape, smoothness, rigidity, elasticity and properties generally of the objects worked with, specifications usually quite impossible to realize in fact, yet absolutely necessary to make, while the disturbing factors are simply anything not included in the specifications, and their actual elimination is probably equally impossible to realize, and, again, equally necessary to assume. Only thus could we ever obtain laws, descriptions of the separate elements of phenomena and their separate behavior. And while such laws, of course, never accurately hold good in any particular case, because they are inplete, not including all the elements in the case, yet they enable us to deal with practical problems intelligently because they are approximately true and we know how to discount their inpleteness. Only by such approximations, reached by dealing analytically with the more important and more universal aspects of phenomena, could we ever have attained any intelligent conception of the behavior of masses of matter in motion and secured our present marvelous mastery over the forces of nature. In a similar way, but for various reasons not so pletely and satisfactorily, we have developed a historic bo