A history of style—I mean of style in general, not of one particular style—has, so far as I am aware, never been written. That I can understand. It would be a gigantic task, even exceeding the power of an encyclopædist. It would have to show from what spiritual peculiarities of the artist; from what necessities and intuitions of the time; from what requirements of the material, and from what compulsion on the part of the technique, the style develops, and it would have to measure the whole range of individual and national psychology, of customs, of material and of technology. The individual, however, whose powers do not suffice for an exhaustive and systematic exposition of the genesis and mutation of styles, can constantly register partial observations, and throw light on sections of this wide province. Every human activity is excited by a need. We fabricate weapons, implements, shelter, and clothing, because we need them. In the earliest stages of human artistic skill, purpose and material alone control the productions of the human hand; style, so far as we can speak of such a thing, is purely constructive. It makes us recognise the influence of a small number of bio-mechanical and psychological laws—laws that have hardly varied during all the thousands of years in the history of human morals. These laws are those of the least effort and of selfishness. By virtue of the law of least effort we choose the most promising material, _i.e._, at which we have most conveniently to hand, which can be worked in the easiest way, or is most durable, and for that reason, more especially saves us the too frequent repetition of the effort. We choose the form to which the material employed adapts itself most readily. The problem which the constructive element in style has to solve is this: given a determined task which should be performed by an artistic expedient, how will this object be most readily, and yet most perfectly, attained with the material available?