How he would have regarded certain liberties in the harmonic progression may be surmised. Although Bach himself was in this respect something of an innovator, he must have deemed such divergence the justifiable limit of rule-breaking. Could he have looked forward to the chief exponent of the Classical School, he might have said, «This Beethoven goes too far, even to the deliberate employment of consecutive, perfect fifths in rash attempt to produce dubious effects. Besides, he abandons the native German domain of the Fugue and debouches upon a land whereof I know not, a strange land of questionable manners and customs.»
Monteverde in his day dared to introduce the unprepared seventh of the dominant triad; but, in boldness he was not alone. In fact, the development of polyphony from the wholly unembellished and quite faulty chord progressions of early mediæval music, has been but a series of innovations at first condemned, then suffered, and then adopted. The earliest polyphonic writers founded their music wholly on the ecclesiastical scales derived from the Greek modes, and approved by Ambrose and Gregory. With the single exception of the Ionic scale, identical with our scale of C major, these scales were defective chiefly in one essential, to wit: in place of the modern sharped seventh, they contained the flatted seventh. This error precluded the possibility of the characterizing major third of the dominant chord in both the major and the minor. Then again, the sounding of the flatted seventh, which in modern tonality indicates modulation to the subdominant key, suggested to the old contrapuntists a triad now deemed wholly foreign to the tonic. The resulting vagueness found remedy where one should least expect it, for, in their melodies, the popular writers of both song and dance were led instinctively to sharp the seventh, and otherwise reconstruct the six defective ecclesiastical scales.
The increasing use of accidentals in contrapuntal and sacred music, gradually evolved the chromatic scale, and led to the founding of a major and a minor scale on each of its twelve semitones. These twenty-four were now the basis of that grand and satisfying instrumental polyphony which Bach was to build in his «Well-tempered Clavichord.»