THIS is an able and interesting volume, in which there is at once great learning and considerable power of speculation. Prof. Catlin has an important thesis to maintain, and his urbanity of manner will not conceal from the reader that he is prepared to maintain his ground against all comers. The field, indeed, is already, as if in advance of conflict, strewn with the illustrious dead; at least I seem to discern there the scalps of Plato and Aristotle, Kant and Hegel, exposed as a warning to prospective combatants. In a sense, Prof. Catlin's book is difficult to review; for it is to be followed by a book already in preparation in which the thesis he here lays down is to be applied to our problems. Obviously, therefore, we shall not fully know what the method he advocates can do until he himself has applied it; and conclusions upon his analysis must be provisional until he has given us the full opportunity to see it at work. But as I understand his views, his purpose is to construct a science of politics which shall seek to do for man in society what the early economists did for the phenomena they survey. It will be abstract and deductive; it will have its axioms and postulates; and the test of its validity will lie in the verifiability of its predictions. Such a science, he argues, must free itself from the shackles which the historian and the philosopher have sought to impose upon it. For values it will have no concern. It will be concerned only with the observed behaviour of men. Assuming that there is a political man with the appetite for power, it will seek to construct the laws of his behaviour in adjusting means to purpose. With right or wrong it will have no more concern than the chemist with the moral qualities of hydrogen. It will be quantitative in character in that, upon the basis of its assumptions, it will seek from observation the largest possible number of examples from which to draw its conclusions. Having made abstraction of ethics, it will be able to approach the facts without a parti pris; and, instead of offering futile sacrifices upon the altar of teleology, it will be able to say (p. 199) that the " social situation only admits of certain appropriate measures." For studying what men do, it will be able to tell us what they will do; between the two Prof. Catlin injects a formidable therefore; and as this science of politics is refreshed by the constant accumulation of facts about the behaviour of men in their desire for power, as, also, such sister sciences as psychology contribute their due quota of knowledge, we may hope for the discovery of truths which will have value and influence of the same magnitude as those to which the economists have given birth.There is an air of promising certitude about these propositions, which have at least the merit of interesting audacity; though I observe with a little surprise that Machiavelli is appealed as their benevolent compurgator. For if ever a man had a definite end in view (which, as a passionate Italian patriot, he would have regarded as ethical), if ever, also, a man selected his facts to suit the thesis his experience dictated as best suited to his end, that man was Machiavelli. Perhaps the best thing one can do is to indicate, though with appreciation, some of the doubts to which Prof. Catlin's argument gives rise. The victories of economic science as built in terms of ' economic man' seem to me less outstanding than he claims, and its main successes have been won in spite of, rather than because of, its original and rigorous abstraction. The chief influence of the late Prof. Marshall, for example, was mainly due to the ingenuity with which he transformed the classic economics into something approaching the complexity of the facts; in no other way, moreover, could the economists answer the challenge of Marx, whose own 'economic man' led, by the technique of his construction, to quite different conclusions. Prof. Catlin, moreover, has a simple faith in facts as such, which, in the social sciences, at least, I do not find it easy to share. They are not born free and equal. The expert interpretation of a social environment is coloured by the personal equation of the observer in a way that is momentously different from an expert interpretation of a physical or chemical environment. What Mr. Justice Holmes has called the ' inarticulate major premiss' of the judiciary is, as a rule, the main clue to their decisions; and yet the best of judges usually believe that they are finding the law in an unbiassed and scientific way. Nor is this all. The maxim 'as men behave, so they will behave,' is, statistically, probably true in a static world; the trouble with this world is that the environment changes at a pace so rapid that the forms of behaviour in one place or period are no clue to those forms in another. I agree that most social situations admit only of certain appropriate measures. But the difficulty here (and I cannot find that Prof. Catlin deals with it) is that the measures have to be chosen in terms of an end deemed right or wrong. We are, in fact, at once outside the realm of scientific politics; for here we are dealing with argument that has reference to ethical value which Prof. Catlin deems irrelevant. I would venture here to add that if the 'political man ' were what he describes him to be, in any sense that can be called significant, he represents so small a proportion of mankind that prediction built upon his behaviour would be no clue to the general habits of men. I wish, indeed, that Prof. Catlin had given us some examples of the political 'laws' that his science would establish. Provisionally, at least, he still leaves me with the impression that Burke's ' little mirror of circumstances ' would be vital in the battle.Perhaps I may put my difficulty in terms of an analogy. The Common Law for long proceeded upon the assumption (akin in character to that of Prof. Catlin) that where there was no remedy there could be no wrong; and in order that it might be adequate and effective it was necessary to invent the remedies of Equity, which proceeded upon the assumption (akin to that of political philosophy) that wrongs as such were entitled to redress. My own conviction is that Prof. Catlin's science of politics would need a similar supplement. What seems to me really valid (and brilliantly demonstrated) in his book is its plea for the systematic collection of facts and the deliberate undertaking of experiment. We need, in fact, an inductive study of politics, based on quantitative tabulation, instead of deductions moulded from our private desires. To have shown with wit and point and learning how much might be expected from such a development is the very considerable service Prof. Catlin has rendered us.