Identifying a Mode by Its Signature Degree

A mode is a seven note scale defined by where its half steps fall relative to its tonic. Major and minor are the two most familiar modes, but Dorian, Phrygian, Lydian, Mixolydian, and Locrian are built from the same kind of material, each with its half steps in a different spot. The fast way to name one is not to build it from scratch but to compare it against the major or minor scale that shares the same tonic, called the parallel major or minor. Each mode differs from its parallel by exactly one raised or lowered degree, and that single difference is its signature.

To find a mode, first find the tonic, the note the melody keeps returning to and resting on. Then compare the melody's notes against the major scale built on that same tonic. If every note matches except the 7th, which is lowered a half step, the mode is Mixolydian. If only the 3rd, 6th, and 7th are lowered compared to major, you likely have natural minor, which is itself the Aeolian mode. Compare against parallel minor instead when a melody looks minor-ish: a raised 6th signals Dorian, and a lowered 2nd signals Phrygian. Lydian is the mirror case against major, with a raised 4th instead of a lowered note at all.

This matters because modal melodies do not announce themselves through key signature the way major and minor keys do. A mode is a question of which note functions as home and which single degree has moved, not which accidentals appear on the staff. This sets up the rest of the unit, where you track how modal color shapes phrases and how those phrases build into the larger forms modal and tonal music both use.