The following remarks come from Arnold Schoenberg's Essay, Composition with Twelve Tones. My amendations appear in brackets throughout.
Composition with Twelve Tones
The method of composing with twelve tones grew out of a necessity.
In the last hundred years, the concept of harmony has changed tremendously through the development of chromaticism. The idea that one basic tone, the root, dominated the construction of chords and regulated their succession - the concept of tonality - had to develop first into the concept of extended tonality. Very soon it became doubtful whether such a root still remained the center to which every harmony and harmonic succession must be referred. Furthermore, it became doubtful whether a tonic appearing at the beginning, at the end, or at any other point really had a constructive meaning. [i.e. what made a tonic a tonic] Richard Wagner's harmony had promoted a change in the logic and the constructive power of harmony. One of its consequences was the so-called impressionistic use of harmonies, especially practised by Debussy. His harmonies, without constructive meaning, often served the coloristic purpose of expressing moods and pictures. Moods and pictures, though extra-musical, thus became constructive elements, incorporated in the musical functions; they produced a sort of emotional comprehensibility. In this way, tonality was already dethroned in practice, if not in theory. This alone would perhaps not have caused a radical change in compositional technique. However, such a change became necessary when there occurred simultaneously a development which ended in what I call the emancipation of the dissonance.
The ear had gradually become acquainted with a great number of dissonances, and so had lost the fear of their 'sense-interrupting' effect. One no longer expected preparations of Wagner's dissonances or resolutions of Strauss' discords; one was not disturbed by Debussy's non-functional harmonies, or by the harsh counterpoint of later composers. This state of affairs led to a freer use of dissonances comparable to the classic composers' treatment of the dimished seventh chords, which could precede and follow any other harmony, consonant or dissonant, as if there were no dissonance at all.
What distinguishes dissonances from consonances is not a greater or a lesser degree of beauty, but a greater or lesser degree of comprehensibility. In my Harmonielehre, [a harmony textbook written by Schoenberg] I presented the theory that dissonant tones appear later among the overtones, for which reason the ear is less intimately acquainted with them. This phenomenon does not justify such sharply contradictory terms as concord and discord. Closer acquaintance with the more remote consonances - the dissonances, that is, - gradually eliminated the difficulty of comprehension and finally admitted not only the emancipation of dominant and other seventh chords, dimished sevenths and augmented triads, but also the emancipation of Wagner's, Strauss's, Moussorgky's, Debussy's, Mahler's, Puccini's, and Reger's more remote dissonances. [Schoenberg is suggesting that what have long been considered dissonances are in reality the higher overtones of the harmonic series. As people became more acquainted with these higher overtones, it became more commonplace to use more adventurous harmonies.]
The term emancipation of the dissonance refers to its comprehensibility, which is considered equivalent to the consonance's comprehensibility. A style based on this premise treats dissonaces like consonances and renounces a tonal center. By avoiding the establishment of a key, modulation is excluded, since modulation means leaving an established tonality and establishing another tonality.
The first compositions of this new style were written by me around 1908 and, soon afterwards by my pupils, Anton von Webern and Alban Berg. From the very beginning such compositions differed from all preceding music, not harmonically but also melodically, thematically and motivally. But the foremost characteristics of these pieces in statu nascendi were their extreme expressiveness and their extraordinary brevity. At the same time, neither I nor my pupils were conscious of the reasons for these features. Later I discovered that our sense of form was right when it forced us to counterbalance extreme emotionality with extraordinary shortness. Thus, subconsciously, consequences were drawn from an innovation which, like every innovation, destroys while it produces. New colorful harmony was offered; but much was lost.
Formerly, the harmony had served not only as a source of beauty, but, more important, as a means of distinguishing the features of the form. For instance, only a consonance was suitable for an ending. Establishing functions demanded different successions of harmonies than roving functions; a bridge, a transition, demanded other successions than a codetta; harmonic variation could be executed intelligently and logically only with due consideration of the fundamental meaning of the harmonies. Fulfillment of all these functions - comparable to the effect of punctuation in the construction of sentences, of subdivision into paragraphs, and of fusion into chapters - could scarcely be assured with chords whose constructive values had not as yet been explored. Hence, it seemed at first impossible to compose pieces of complicated organization or of great length.
A little later I discovered how to construct larger forms by following a text or a poem. The differences in size and shape of the parts and the change in character and mood were mirrored in the shape and size of the composition, in its dynamics and tempo, figuration and accentuation, instrumentation and orchestration. Thus the parts were differentiated as clearly as they had formerly been by the tonal and structural functions of harmony. [By following a text, Schoenberg could allow the text to dictate the form, rather than something that involved tonality, such as a Sonata.]
Formerly the use of the fundamental harmony had been thoeretically regulated through recognition of the effects of root progressions. [as in basso continuo] This practice had grown into a subconsciously functioning sense of form which gave a real composer an almost somnambulistic sense of security in creating, with utmost precision, the most delicate distinctions of formal elements.
Whether one calls oneself conservative or revolutionary, whether one composes in a conventional or progressive manner, whether one tries to imitate old styles or is destined to express new ideas - whether one is a good composer or not - one must be convinced of the infallibility of one's own fantasy and one must belive in one's own inspiration. Nevertheless, the desire for a conscious control of the new means and forms will arise in every artist's mind; and he will wish to know consciously the laws and rules which govern the forms which he has conceived 'as in a dream'. Strongly convincing as this dream may have been, the conviction that these new sounds obey the laws of nature and our manner of thinking - the conviction that order, logic, comprehensibility and form cannot be present without obedience to such laws - forces the composer along the road of exploration. He must find, if not laws or rules, at least ways to justify the dissonant character of these harmonies and their successions.
After many unsuccessful attempts during a period of apporximately twelve years, I laid the foundations for a new procedure in musical construction which seemed fitted to replace those structural differentiations provided formerly by tonal harmonies.
I called this procedure Method of Composing with Twleve Tones Which are Related Only with One Another.
This method consists primarily of the constant and exclusive use of a set of twelve different tones. This means, of course, that no tone is repeated within the series and that it uses all twelve tones of the chromatic scale, though in a different order. It is in no way identical wiith the chromatic scale.....[The method involves ordering the twelve tones of the chromatic scale into a row, known as the Basic Set, and using that row and its properties exclusively throughout the composition in question.]
The introduction of my method of composing with twelve tones does not facilitate composing; on the contrary, it makes it more difficult. .....
It has been mentioned that the basic set is used in mirror forms.
Form the basic set, three additional sets are automatically derived: (1) the inversion; (2) the retrograde; and (3) the retrograde inversion. The employment of these mirror forms coressponds to the principle of the absolute and unitary perception of musical space. [these "mirror forms" correspond to the ways that composers dealt with fugue subjects. Being derived from the basic set, they provide contrast to it and unity with it. It is worth noting that the relation between the Basic Set and its Inversion is the same as between a Major Scale and a Minor Scale.]
The main advantage of this method of composing with twelve tones is its unifying effect....
For Richard Wagner, operas consisted almost exclusively of independent pieces, whose mutual relation did not seem to be a musical one. Personally, I refuse to believe that in the great masterworks [of opera, such as Don Giovanni, or Orfeo] pieces are connected only by the superficial coherence of the dramatic proceedings. Even if these pieces were merely 'fillers' taken from earlier works of the same composer, something must have satisfied the master's sense of form and logic. We may not be able to discover it, but certainly it exists. In music there is no form without logic, there is no logic without unity.
I believe that when Richard Wganer introduced his Leitmotiv - for the same purpose as that for which I introduced my Basic Set - he may have said: 'Let there be unity.'
from Arnold Schoenberg, "Composition with Twelve Tones" in Leonard Stein, ed. Style and Idea (Berkeley, 1975) 216 - 244.