--Perhaps the most inveterate of these modern habits of musical thought is the harmonic habit. It is second nature for us to conduct all our musical thinking in terms of harmonic relations. We think of chords as related to one another in certain fixed ways, as forming groups or clusters just as definite as the groups of atoms in a chemical molecule. It is not more sure, for example, that in a molecule of water two atoms of hydrogen are engaged or held in combination by one atom of oxygen, than it is that in any key the dominant and sub-dominant chords are held in the position of subordinate companions by the tonic chord, and that the other chords of the key are held in more remote but still perfectly fixed relations with this Paterfamilias of the harmonic family. We think of the chords in a phrase, of whatever length and complexity, as progressing in a coherent series, as intertwined one with another by manifold relationships, and as embodying, all together, some one key. For us, every composition is in some particular key as inevitably as every poem or essay is in some particular language. We modulate freely, to be sure, from key to key; but this rather intensifies than obliterates our sense of key, just as the process of translating from one language to another intensifies our sense of the peculiar idioms of each. Our whole manner of thought would be as indescribably shocked by a passage which placed together, cheek by jowl, chords belonging to different keys, as by a sentence every word of which was drawn from a different tongue.