You know... I don't really know the names of the modes for the minor pentatonic scale. They're really abstract only having 5 notes. I never really play modally out of the pentatonic scale usually just positionally, but assuming Em as your theme, E Dorian, E Phrygian, and E Aeolian will work over it. Obviously, it depends on what other chords (or notes) you have in this Em theme that best determine what mode will sound best over it.

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