A scale is an ordered set of notes. A key is the scale a piece of music is centred on, named after the note it treats as home. Nearly everything else in written music, the tune, the bassline, the chords, is chosen from the handful of notes a key gives you, which is why the two ideas are worth getting straight before anything else.
Plain theory, no instrument required. It works the same on a piano, a guitar, or in a piano roll, in any key and any style.
A scale is an ordered set of notes, drawn from the twelve pitches available in Western music, that a piece mostly draws on. Choose a starting note and a fixed pattern of steps, and the scale is the row of notes that pattern produces.
Those twelve pitches are the raw material. Inside one octave, the distance from a note up to the next note of the same name, there are twelve of them before you arrive back where you started. On a piano they are the seven white keys and five black keys: C, C# (or Db), D, D# (or Eb), E, F, F# (or Gb), G, G# (or Ab), A, A# (or Bb), B, and then C again. Those twelve in order are the chromatic scale, and the gap between one and the next is a semitone, the smallest step in this system. Two semitones make a tone, also called a whole step.
Almost every scale you meet is a particular selection of seven of those twelve, spaced by a fixed pattern of tones and semitones. So a scale is really just two things: a note to start on, and the pattern of steps that walks you up from it.
A key is the scale a piece of music is centred on, together with the note it treats as home. That home note is the tonic, and the key is named after it, so a piece in C major is centred on C and draws on the C major scale.
The major scale is the most common pattern of all. Starting from its home note, the steps go
tone, tone, semitone, tone, tone, tone, semitone, written W W H W W W H for whole
and half steps. Apply that to C and you get C, D, E, F, G, A, B, then back to C, which happens to
land on only the white keys of a piano. That is C major.
| Step | Note | To the next |
|---|---|---|
| 1 | C | Tone |
| 2 | D | Tone |
| 3 | E | Semitone |
| 4 | F | Tone |
| 5 | G | Tone |
| 6 | A | Tone |
| 7 | B | Semitone |
| 8 | C | Home again |
Start the same pattern on a different note and you get a different major key, using whatever sharps or flats it takes to keep the spacing identical. The note names change; the shape does not. That is the whole value of thinking in keys rather than loose notes.
Major and minor are two different step patterns, and the difference in their spacing is what makes major tend to sound bright while minor tends to sound darker or sadder. Same twelve notes to choose from, a different arrangement of tones and semitones between them.
The natural minor scale follows the pattern tone, semitone, tone, tone, semitone, tone, tone,
or W H W W H W W. Start it on A and you get A, B, C, D, E, F, G, then back to A,
which once again lands on only the white keys. That is A minor.
Look closely and something useful appears: C major and A minor contain exactly the same seven notes. They only begin in different places and treat a different note as home. Two keys that share a set of notes like this are called relative. A minor is the relative minor of C major, and C major is the relative major of A minor; every major key has a relative minor built on the sixth note of its scale.
| Key | Notes | Pattern |
|---|---|---|
| C major | C D E F G A B | W W H W W W H |
| A minor | A B C D E F G | W H W W H W W |
C major and A minor are the two keys that need no sharps or flats at all; every other key raises or lowers certain notes to hold the same pattern from a different starting note, and the circle of fifths is simply the map that orders the keys by how many sharps or flats they carry, adding one more at each step of a fifth.
Staying inside one scale is the main reason a group of notes sounds "right" together. When a melody, a bassline and the chords under them all draw from the same seven notes, they agree by default, and the ear reads them as belonging to one piece.
This is why choosing a key first is such a useful move. It narrows the twelve notes down to the seven that fit, so you can write a tune, improvise, or harmonise and trust that what you play will sit inside the same family of sound. Notes from outside the key are not forbidden, and they can be lovely, but they stand out, which is exactly why they tend to be used sparingly and on purpose.
The chords of a piece are built from the notes of its key as well, which is why picking a key comes before almost everything. Our guide to writing a chord progression takes the scale from here and stacks it into the chords a key hands you.
If you want the safest possible version of all this, a pentatonic scale trims a key down to five notes by dropping the two that clash most, so the major pentatonic is just a major scale without its fourth and seventh, leaving C, D, E, G, A in C major, which is why it is so hard to hit a wrong note with one.
We built ARGISH to make a scale audible. It is a self-playing synth locked to a key: pick a key and a mood, and every note it generates stays inside that scale, so the whole thing simply sounds right without you placing a single note or knowing any of the theory. It is the quickest way to hear what a key actually sounds like, and to feel the difference between major and minor by ear.
It runs free in your browser to try, and installs as AU, VST3, AAX or a standalone app when you want it inside your own sessions.
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