Imperfect Tense

What was going on?
What used to be?
 
Compare: primary endings for present tense
Compare: secondary endings for imperfect

Present Tense    Imperfect Tense
stem + primary endings augmented stem + secondary endings
  am setting free   λύ ω   was setting free   λυ ον
you    are setting free   λύ εις you   were setting free λυ ες
He   is setting free λύ ει he   was setting free λυ ε (ν)
We   are setting free λύ ομεν we   were setting free λύ ομεν
You   are setting free λύ ετε you   were setting free λύ ετε
They    are setting free λύ ουσιν they   were setting free λυ ον

Note the movable ν in the 3rd person singular used at the end of a clause, or before words starting with a vowel.