The chromatic scale, intervals, chords, keys, and modes — interactive
Western music uses 12 evenly-spaced pitches that repeat in octaves: C, C#, D, D#, E, F, F#, G, G#, A, A#, B, then back to C. A scale picks 7 of them, a chord stacks 3 or 4, and a key is the family of scales and chords that hang together. The Circle of Fifths below is the map for moving between keys.
Each section is interactive. Click around. The Bass and Guitar pages let you see these notes on a fretboard.
Each step clockwise raises the tonic by a fifth and adds one sharp; each counterclockwise step drops by a fifth and adds a flat. Adjacent keys share six of their seven notes, which is why so many songs modulate between neighbors. The inner ring is the relative minor — same key signature as the major above it.
An interval is the distance between two notes measured in semitones. A chord is a stack of intervals from a root. The major triad is R + M3 + P5 (a 4-semitone jump then a 3-semitone jump). Swap M3 for m3 and you have a minor triad. Add m7 on top and it becomes a dominant 7. Pick a root, then click intervals to stack them.
Every major key produces the same pattern of chords on its seven scale degrees: I ii iii IV V vi vii°. Three major, three minor, one diminished — always in that order. Most songs in a major key cycle between these seven chords; learning the pattern in one key teaches you the pattern in all of them.
A mode takes the seven notes of a parent major scale and starts the home note on a different degree. Same notes, different home — which puts the half-steps in different places and changes the whole feel. Pick a parent key to see all seven modes derived from it.
Sharps always appear in the same order: F C G D A E B ("Father Charles Goes Down And Ends Battle"). Flats are the reverse: B E A D G C F. Each new key in the circle adds the next accidental in the sequence. To name the major key from a sharp signature, take the last sharp and go up a half-step. From a flat signature, the second-to-last flat is the key.