Ionian Mode

The Ionian mode is the major scale under its modal name. On the white keys it runs from C to C: C D E F G A B C. Its step pattern is the familiar one:

W – W – H – W – W – W – H

▶C Ionian (white keys)0:07▶G Ionian = G major0:06

Why two names for one scale?

You will hear "Ionian" mostly when musicians talk about the modes as a family. Listing the seven side by side (Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, Locrian) shows that each one is a rotation of the same pattern, and Ionian is the starting point: Dorian begins on its 2nd degree, Phrygian on its 3rd, and so on. In everyday playing and writing, "major scale" is by far the more common name.

In jazz theory, Ionian names the chord-scale for a major chord on the tonic, usually a major seventh chord (Cmaj7 in C). Jazz players often treat the 4th degree, F over Cmaj7, as an "avoid note" to pass through rather than hold, because it clashes a half step above the chord's 3rd.

Its place among the major modes

Of the three major-sounding modes, Ionian sits in the middle. Lydian raises its 4th (F♯ in C) and sounds brighter; Mixolydian lowers its 7th (B♭ in C) and sounds earthier. Ionian is the only one of the three with both a perfect 4th and a leading tone a half step below the tonic, and that gives it the strongest pull toward home: the dominant chord (G or G7) resolving to the tonic C is the sound of a major key.

A bit of history

Ionian was not among the eight modes of medieval chant theory. The Swiss theorist Heinrich Glarean added it, together with the Aeolian, in his treatise Dodecachordon of 1547. Over the following century and more, music in this mode developed into what we now call the major key.

Finding Ionian in any key

There is nothing to work out: E♭ Ionian is E♭ major, F♯ Ionian is F♯ major, and the key signature is the same. Use the major-scale step pattern, or Scales in Every Key, and you have it. The modes shows how the other six modes grow out of it.