Which mode has half steps between 4-5 and 7-8 and starts on the fourth degree of the major scale (for example, white keys from F to F)?

• A. Lydian mode
• B. Mixolydian mode
• C. Dorian mode
• D. Phrygian mode

Answer: (A)

This mode is defined by a raised fourth scale degree compared to the major scale. That single change makes the interval from the fourth to the fifth degree a half step, while the interval from the seventh to the octave remains a half step as in any major-scale family. In practice, starting on the fourth degree of the major scale, such as F in C major, you get F–G–A–B–C–D–E–F. Here, B to C is a half step (4–5) and E to F is a half step (7–8), exactly matching the described pattern. That combination of half steps at those exact locations is the hallmark of this mode. Other modes do not produce both 4–5 and 7–8 as half steps, so they don’t fit this pattern. Therefore, the mode is Lydian.