Uh—Ionian, actually. Relative to what we now call a major scale [C D E F G A B C], the Lydian mode has a raised fourth degree. [C D E F# G A B C]. Frank Zappa notwithstanding.

The second most common mode is the Aeolian, which we call the "natural minor."

Modes are not that mysterious and difficult. They are just the usual scales with the order of steps and half-steps modified a bit. For example, take the natural minor (Aeolian mode) [A B C D E F G A], raise the sixth degree of the scale a half-step, [A B C D E F# G A], and you have the Dorian mode. Take the major scale (Ionian mode), [C D E F G A B C], lower the seventh degree a half step, [C D E F G A Bb C], and you have the Mixolydian mode.

Apart from giving the melody line a little spice, what really makes a difference in the sound is if you make sure that the guitar (or whatever) chords are made up only of notes from the mode itself.

Don Firth