The ultimate significance of a work of art is its content of emotion, the essential controlling idea, which inspires the work and gives it concrete form. In its actual embodiment, the expressive power of the work resides in the medium. The medium of any art, then, as color and mass in painting, line in drawing and etching, form in sculpture, sound in music, is its means of expression and constitutes its language. Now the signification of language derives from convention. Line, for example, which may be so sensitive and so expressive, is only an abstraction and does not exist in nature. What the draughtsman renders as line is objectively in fact the boundary of forms. A head, with all its subtleties of color and light and shade, may be represented by a pencil or charcoal drawing, black upon a white surface. It is not the head which is black and white, but the drawing. Our acceptance of the drawing as an adequate representation of the head rests upon convention. Writing is an elementary kind of drawing; the letters of the alphabet were originally pictures or symbols. So to-day written or printed letters are arbitrary symbols of sounds, and grouped together in arbitrary combinations they form words, which are symbols of ideas. The word _sum_ stood to the old Romans for the idea "I am;" to English-speaking people the word signifies a "total" and also a problem in arithmetic. A painting of a landscape does not attempt to imitate the scene; it uses colors and forms as symbols which serve for expression. The meaning attaching to these symbols derives from common acceptance and usage, Japanese painting, rendering the abstract spirit of movement of a wave, for example, rather than the concrete details of its surface appearance, differs fundamentally from the painting of the western world; it is none the less pregnant with meaning for those who know the convention. To understand language, therefore, we must understand the convention and accept its terms. The value of language as a means of expression and communication depends upon the knowledge, common to the user and to the person addressed, of the signification of its terms. Its effectiveness is determined by the way in which it is employed, involving the choice of terms, as the true line for the false or meaningless one, the right value or note of color out of many that would almost do, the exact and specific word rather than the vague and feeble; involving also the combination of terms into articulate forms. These ways and methods in the use of language are the concern of technique. Technique, therefore, plays an important part in the creation and the ultimate fortunes of the artist's work.