is th at element of key-feeling which was gradually evolved out of the increasingly harmonic organisation of modal polyphony. In the end it completely supplanted the less universal values which had depended on the particular character of a particular mode. Throughout the whole development of classical forms key-definition has occupied a paramount place, and without it neither the harmonies nor the architecture of the music of the last three centuries can be made intelligible. Tonality in general rests mainly on a balance of tonic harmonies rendered stable and convincing by the use of a context of such related or leading chords as appear to find their ultimate solution in the desired key. Of these leading chords those of the dominant of the key in question are the most important, and a satisfying definition is almost impossible without harmonic inferences which are ultimately derived from the relation between the chosen key and its dominant. Subdominant harmonies also have harmonic inferences which can be used to consolidate a tonality, though these are not so powerful as those of the dominant. The simplest definitions of a tonality are to be found in the various cadences which were organised to this end. Examples will be found in the articles on Ca d en c e and H armony. Those extended forms of the sonata order on which classical instrumental music has been mainly built, have acknowledged an unqualified allegiance to rigid tonalities. And this is almost equally true of every musical form which has an intrinsic architectural coherence. Keys and their relations are in this sense the postulates on which melodic, harmonic and formal arguments were alike founded, and it was by an unfailing sensitiveness to these values th a t composers were able to display a wealth of imaginative fancy and yet preserve a formal balance and coherence th a t made an extended movement an artistically proportioned whole (see F o rm ; S onata). I t must be admitted, however, th a t three centuries of development have not left these fundamental conceptions of tonality altogether unqualified. Dramatic music in particular has always claimed a certain freedom to obey ideas external to music proper, and has therefore subjected many formal considerations to demands of an alien kind. Moreover, increasing familiarity with idioms thus externally suggested has made it possible to transfer even to the most absolute music a noticeable licence in the treatment of keys and their definitions. I Opera and programme music alike have shown this power of indirect infection. I t must further be remembered th a t the more sensitive the mind of the composer may be to the inferences of tonality, the more novel and subtle are likely to be the relations which he will comprehend within it. There can be no doubt th a t many of the idioms which the 19th century has accepted as having a clear basis in tonality would have appeared to the musicians of an earlier day too vague and fantastic to be intelligible on any traditional principles. And to this must be added the fact th a t the very strength of the tonal organisation which three centuries of masterpieces has inculcated, has served to give a certain attraction to devices of expression not so rigidly proportioned. There has recently been a decided renaissance of such values as belonged to more modal systems, and whether these are practised as a form of conscious archaism, or are less directly culled from the half-forgotten idioms of folkmusic, they are equally subversive of keydefinition in the stricter classical sense. Nor have contemporary composers scrupled to derive novel idioms from various arbitrarily chosen formulae, many of which are deliberate negations of the traditional associations of tonality. Some of the consequences of these phenomena have been outlined in the article on H armony. The word atonality has recently been coined to describe these non-tonal idioms. I t is not of much use for purposes of exact description, because it logically includes modal, neo-modal, and all kinds of arbitrary melodic or h a r monic dialects, even to the degree of complete chromaticism. These various features have been dealt with under their respective headings, and in the article on H armony. Polytonality is a synonym for Multiple Tonality, and refers to certain features of contemporary experiment in which more than one tonality is involved in a single harmonic structure. This also is discussed in the article on H arm ony. g . d .