Tonality

Play these notes and stop:

Hear the passage

The last note hangs in the air. Almost anyone who hears it wants one more note, and knows which: the G above.

Hear the passage

Nothing in the notes themselves says G is special. The ear decides that, because everything before it has been arranged around G. That arrangement, one note as the centre and every other note and chord placed in relation to it, is tonality.

What the books mean by it

Lacerda starts from how music is usually built: a melody takes its notes from a major or minor scale, and the chords that accompany it are built on the same scale. The degrees of that scale then take on functions, and they are not equal: the first degree, the tonic, is the principal one, followed in importance by the fifth, the dominant, and the fourth, the subdominant. Tonality is the name for that whole set of functions, of the degrees and of the chords built on them (Lacerda 1966, ch. XXVI).

Med gathers several definitions that say the same thing from different sides: the dependence of every degree on the tonic, the centre of all movement; the body of sounds and chords that refer to a main centre; the set of functions of the degrees and their chords. He adds a short definition of tonal music: music in which the sounds have a hierarchy and a centre of attraction can be heard (Med 1996, ch. XV).

Key and tonality

In English, "key" covers most of this: a piece is "in G major". Portuguese books split the idea in two, and Med makes the split explicit. Tonalidade, tonality, is the system: major or minor, the hierarchy itself. Tom, key, is that system placed at a particular pitch: the key of G, the key of B flat (Med 1996, ch. XV). A key uses the notes of its scale, but in any order the music wants.

A tonality takes its name from the scale it is built on: a passage built on the B flat minor scale is in B flat minor (Lacerda 1966, ch. XXVI).

The degrees that fix the centre, and the ones that colour it

Play D major and D minor side by side.

Hear the passage

Hear the passage

The first, fourth and fifth degrees, D, G and A, are the same in both. Blatter points out what that means for the ear: if a piece used only those three notes, you could not tell whether it was in major or minor. So the tonic, subdominant and dominant are called tonal degrees: they establish where the centre is. The third, sixth and seventh degrees change between the two, and they are the ones that tell the listener which mode it is; they are called modal degrees. The second has something of both (Blatter 2007, part 2, art. 8). Med gives the same trio, I, IV and V, as the degrees that define the key, noting that they form perfect intervals with the tonic (Med 1996, ch. XV).

Every note leans somewhere

Inside a tonality the notes are not neutral. Some are points of rest, others want to move. Blatter describes the strongest tendencies (Blatter 2007, part 2, art. 8):

• the leading tone, the seventh degree, pulls up to the tonic;
• the supertonic, the second degree, at the end of a descending line, wants to fall to the tonic;
• a melody that stops on the dominant sounds unfinished, and is satisfied by reaching the tonic, by step or by leap;
• in major, the subdominant tends to fall to the third degree.

Hear the passage

In G major, the four pulls in order: seventh to tonic, second to tonic, dominant down to the tonic through the third and second, fourth to third. The tonic, the third and, to a lesser degree, the fifth are where a melody comes to rest; the other notes are the active ones.

Leaving the main key, and coming back

Most pieces do not stay in one key from start to finish. Lacerda describes the usual course: the music begins in a main key, moves through other keys, and returns to the main key to end. Each change of key along the way is a modulation, and when a new key lasts long enough the key signature itself may change (Lacerda 1966, ch. XXVI).

The main key is also the one a reader wants to identify first. A key signature narrows it to a major key and its relative minor; the lowest note of the last chord usually decides between the two; and in a melody without chords, a raised seventh degree near the beginning or the end points to the minor (Lacerda 1966, ch. XXVI).

What comes next

Keys are not all equally far from one another. Some share almost all their notes with the main key and are easy to reach and leave; others are distant. Those closest neighbours are the closely related keys.