Ionian mode
The first mode of the major scale, identical to the major scale itself
In Depth
The Ionian mode is the major scale by another name: its interval pattern is W-W-H-W-W-W-H. In the medieval modal system, Ionian was not officially recognised until the 16th century, when theorist Heinrich Glarean added it and the Aeolian mode to the original eight church modes. Despite being the most familiar Western scale, calling it Ionian rather than major serves a purpose: it places it within the modal system alongside its six siblings, emphasising that major and minor are modes among equals.
Glarean's addition of the Ionian and Aeolian modes in 1547 effectively created the modern major-minor system, though it took another century to fully displace the older modal thinking.