THREE:Thus, then, the Socratic dialogue has a double aspect. It is, like all philosophy, a perpetual carrying of life into ideas and of ideas into life. Life is raised to a higher level by thought; thought, when brought into contact with life, gains movement and growth, assimilative and reproductive power. If action is to be harmonised, we must regulate it by universal principles; if our principles are to be efficacious, they must be adopted; if they are to be adopted, we must demonstrate them to the satisfaction of our contemporaries. Language, consisting as143 it does almost entirely of abstract terms, furnishes the materials out of which alone such an ideal union can be framed. But men do not always use the same words, least of all if they are abstract words, in the same sense, and therefore a preliminary agreement must be arrived at in this respect; a fact which Socrates was the first to recognise. Aristotle tells us that he introduced the custom of constructing general definitions into philosophy. The need of accurate verbal explanations is more felt in the discussion of ethical problems than anywhere else, if we take ethics in the only sense that Socrates would have accepted, as covering the whole field of mental activity. It is true that definitions are also employed in the mathematical and physical sciences, but there they are accompanied by illustrations borrowed from sensible experience, and would be unintelligible without them. Hence it has been possible for those branches of knowledge to make enormous progress, while the elementary notions on which they rest have not yet been satisfactorily analysed. The case is entirely altered when mental dispositions have to be taken into account. Here, abstract terms play much the same part as sensible intuitions elsewhere in steadying our conceptions, but without possessing the same invariable value; the experiences from which those conceptions are derived being exceedingly complex, and, what is more, exceedingly liable to disturbance from unforeseen circumstances. Thus, by neglecting a series of minute changes the same name may come to denote groups of phenomena not agreeing in the qualities which alone it originally connoted. More than one example of such a gradual metamorphosis has already presented itself in the course of our investigation, and others will occur in the sequel. Where distinctions of right and wrong are involved, it is of enormous practical importance that a definite meaning should be attached to words, and that they should not be allowed, at least without express agreement, to depart from the recognised acceptation: for such words, connoting as they do the approval or disap144proval of mankind, exercise a powerful influence on conduct, so that their misapplication may lead to disastrous consequences. Where government by written law prevails the importance of defining ethical terms immediately becomes obvious, for, otherwise, personal rule would be restored under the disguise of judicial interpretation. Roman jurisprudence was the first attempt on a great scale to introduce a rigorous system of definitions into legislation. We have seen, in the preceding chapter, how it tended to put the conclusions of Greek naturalistic philosophy into practical shape. We now see how, on the formal side, its determinations are connected with the principles of Socrates. And we shall not undervalue this obligation if we bear in mind that the accurate wording of legal enactments is not less important than the essential justice of their contents. Similarly, the development of Catholic theology required that its fundamental conceptions should be progressively defined. This alone preserved the intellectual character of Catholicism in ages of ignorance and superstition, and helped to keep alive the reason by which superstition was eventually overthrown. Mommsen has called theology the bastard child of Religion and Science. It is something that, in the absence of the robuster parent, its features should be recalled and its tradition maintained even by an illegitimate offspring.By assuming this or any other well-proved example, and estimating larger or smaller shafts by keeping their diameters as the cube root of the power to be transmitted, the distance between bearings as the diameter, and the speed inverse as the diameter, the reader will find his calculations to agree approximately with the modern practice of our best engineers. This is not mentioned to give proportions for shafts, so much as to call attention to accidental strains, such as winding belts, and to call attention to a marked discrepancy between actual practice and such proportions as would be given by what has been called the measured or determinable strains to which shafts are subjected.