Tone and semitone

The seven note names follow one another like the steps of a staircase. But the steps of this staircase are not all the same height. Play C4 and then D4. Now play E4 and then F4. Both times you went up to the next name, but the second step is shorter: the two notes sit closer together.

Those two measurements have names. The short step is the semitone, and the long step, made of two semitones, is the tone.

The semitone

The semitone is the smallest distance between two notes used in Western music. On the piano it is the distance from one key to the key right next to it, with no other key in between, whether that neighbour is white or black.

Hear the notes

There is no black key between E and F. The two white keys touch, and that is why the distance between them is a semitone. The same happens between B and C:

Hear the notes

A semitone is also called a half step, and a tone a whole step; American books tend to use the second pair of names. Lacerda introduces the semitone just like this, as the difference in pitch between two adjacent piano keys (Lacerda 1966, ch. XVII).

The tone

A tone is the sum of two semitones. On the keyboard it is the distance from one key to the second key after it, skipping one.

Hear the notes

There is a black key between C and D. From C to that black key is one semitone, and from it to D is another. Two semitones, one tone.

The seven names, measured

Now every step between the note names can be measured. Climb from C to the next C on the white keys and notice where a black key sits in between:

Hear the notes

From	To	Distance
C	D	tone
D	E	tone
E	F	semitone
F	G	tone
G	A	tone
A	B	tone
B	C	semitone

The rule shows itself: where a black key sits between two white keys, the distance is a tone; where the white keys touch, it is a semitone. Among the seven names there are only two semitones, E–F and B–C. Because they fall between notes with no sign attached, they are called natural semitones.

Those two pairs are worth remembering. Almost everything that follows, from scales to intervals, depends on knowing where they fall.

Why the black keys are where they are

The layout of the keyboard is not a whim; it is this same pattern. Blatter tells the story from the side of notation: when the system had only the seven natural names, the steps of a tone left room for a sound in between, and notes were added there, which on the keyboard became the black keys; between E and F, and between B and C, the step was already a semitone and nothing fitted (Blatter 2007, art. 2).

That is why the black keys come in groups of two and three. The group of two sits among C, D and E; the group of three among F, G, A and B. The gap between one group and the next is exactly where a natural semitone lives.

Hear the two steps

On paper the two steps look the same: from a line to the next space. Only the ear, or the keyboard, shows the difference.

Hear the passage

The first two distances are tones and the last one is a semitone. Sing along and notice how much less your voice moves on the last step.

The black keys are notes too, and from any key to its neighbour the distance is always a semitone. From F to the black key just above it is a semitone; from E to F, too. Black keys have no names of their own: they use the same seven names with a sign added, and those signs are the subject of accidentals.

What comes next

The books disagree about where this subject belongs. Med puts it early, right after note values, in the same chapter as the signs that alter notes. Lacerda keeps it for the part of his book about pitch and presents it as the smallest of the intervals. The two choices point to the two paths that leave from here: accidentals, which name the black keys by moving a note up or down a semitone, and the interval, which measures the distance between any two notes.