FORE:All these things constitute technical knowledge, and the privilege of their acquirement is an element of value. The common view taken of the matter, however, is that it costs nothing for a master to afford these privilegesthe work must at any rate be carried on, and is not retarded by being watched and learned by apprentices. Viewed from any point, the privileges [22] of engineering establishments have to be considered as an element of value, to be bought at a price, just as a ton of iron or a certain amount of labour is; and in a commercial sense, as an exchangeable equivalent for labour, material, or money. In return a master receives the unskilled labour or service of the learner; this service is presumed to be given at a reduced rate, or sometimes without compensation, for the privileges of the works and the instruction received.The systems of Plato and Aristotle were splendid digressions from the main line of ancient speculation rather than stages in its regular development. The philosophers who came after them went back to an earlier tradition, and the influence of the two greatest Hellenic masters, when it was felt at all, was felt almost entirely as a disturbing or deflecting force. The extraordinary reach of their principles could not, in truth, be appreciated until the organised experience of mankind had accumulated to an extent requiring the application of new rules for its comprehension and utilisation; and to make such an accumulation possible, nothing less was needed than the combined efforts of the whole western world. Such religious, educational, social, and political reforms as those contemplated in Platos Republic, though originally designed for a single city-community, could not be realised, even approximately, within a narrower field than that offered by the mediaeval church and the feudal state. The ideal theory first gained practical significance in connexion with the metaphysics of Christian theology. The place given by Plato to mathematics has only been fully justified by the develop2ment of modern science. So also, Aristotles criticism became of practical importance only when the dreams against which it was directed had embodied themselves in a fabric of oppressive superstition. Only the vast extension of reasoned knowledge has enabled us to disentangle the vitally important elements of Aristotles logic from the mass of useless refinements in which they are imbedded; his fourfold division of causes could not be estimated rightly even by Bacon, Descartes, or Spinoza; while his arrangement of the sciences, his remarks on classification, and his contributions to comparative biology bring us up to the very verge of theories whose first promulgation is still fresh in the memories of men.