In this lesson
A semitone, or half step, is the pitch interval between neighbouring piano keys, including black keys. A tone, or whole step, is two semitones. These distances help you build scales and read altered notes.
This lesson uses the usual twelve-semitone octave. In equal temperament, the octave is divided into twelve equal semitones; other tuning systems and smaller pitch divisions also exist.
Semitones and tones
The white-key names repeat C, D, E, F, G, A, B, then C again. Count the moves between keys, including black keys. From C to C♯ is one semitone. From E to F is also one semitone, because no black key lies between them. B to the next C is the other natural-note pair a semitone apart.
A tone takes two such moves. C to D passes through C♯, so it spans a tone. The keyboard diagram also marks A♯/B♭ to C and F♯/G♭ to G♯/A♭ as tones. Its red examples are semitones; its blue examples are tones.
| Term used in the UK | Equivalent term | Distance |
|---|---|---|
| Semitone | Half step | One adjacent-key move |
| Tone | Whole step | Two adjacent-key moves |
On a conventionally fretted guitar, moving one fret towards the body on the same string raises the pitch by one semitone; two frets raise it by a tone. Keep to one string for this comparison.
Apply this rule in finding guitar fretboard notes, with an open-string-to-fret-5 chart and note-finding exercises.
The word “step” alone can mean movement to the next note of a scale. That movement is not always a semitone. Likewise, adjacent positions on the staff follow letter names, whose pitch gaps vary.
Accidentals
An accidental specifies how a written note differs from its natural letter-name pitch. On the staff, place the sign before the notehead, at that note’s line or space. When writing a name in text, put the sign after the letter: G♯ means G sharp.
| Sign | Name | Meaning relative to the named natural note |
|---|---|---|
| 𝄫 or ♭♭ | Double flat | Lower by two semitones |
| ♭ | Flat | Lower by one semitone |
| ♮ | Natural | Use the natural letter-name pitch |
| ♯ | Sharp | Raise by one semitone |
| 𝄪 | Double sharp | Raise by two semitones |
These signs specify the resulting pitch; they do not accumulate each time they appear. A G♯ is one semitone above G natural, even if a previous G♯ has already appeared.
Flats
The three examples show G♭, B♭ and F♭. On an equal-tempered keyboard, G♭ uses the same key as F♯, B♭ the same key as A♯, and F♭ the same key as E. A flat therefore does not always mean a black key.
Sharps
These examples show G♯, F♯ and E♯. G♯ shares a keyboard key with A♭; F♯ shares one with G♭. E♯ uses the F key, one semitone above E. A sharp does not always mean a black key either.
Double accidentals and naturals
G double flat is two semitones below G natural, sharing the F key. G double sharp is two semitones above G natural, sharing the A key. Measure each alteration from G natural.
A natural sign restores the unaltered letter-name pitch. For example, G♮ after G♯ means G natural. A natural can also override a sharp or flat supplied by the key signature.
Enharmonic spelling
Notes with different names but the same pitch are enharmonic equivalents. The diagram compares G♯ and A♭. In equal temperament they sound alike, while their written letters describe different scale positions.
Spelling follows the musical context. In E major, write the third degree as G♯: E, F♯, G♯, A, B, C♯, D♯, E. This uses each letter once before repeating E. Writing A♭ in place of G♯ would repeat A and omit G. A key that uses sharps does not make every note sharp: G major, for example, has F♯ in its key signature and G natural as its tonic.
How long an accidental applies
In ordinary common-practice notation, a local accidental applies to later notes of the same letter and octave on that staff until the bar ends, unless another accidental changes it. It does not automatically alter that letter in every octave.
For example, with no key signature, an F♯ followed later in the same bar by another F at the same octave makes both notes F♯. Write F♮ to restore F natural within that bar.
At the next bar, return to the key signature’s default. In G major, F♮ in one bar does not permanently cancel the signature’s F♯. A tie across a bar line sustains its existing pitch; a later separate note follows the new bar’s accidental rules. Courtesy accidentals may restate a pitch to make the reading clearer.
In this example, the signature supplies F♯ in every octave. Bar 1 gives F4, F4, F♯5 and G4; bar 2 gives F♯4, G4, A4 and B4. All eight notes are quarters. These are written pitches, with middle C labelled C4; conventional guitar notation sounds one octave lower.
Continue with the major scale to use tones and semitones in a complete pattern.
References: Open Music Theory’s half steps, whole steps and accidentals and Steinberg’s common-practice accidental rules.