Here are the main uses of the imperfect subjunctive:
1. To express doubt, uncertainty or possibility about something in the past.
2. To express wishes, desires or emotions about something hypothetical or unlikely in the past.
3. To express reactions to something that was said or implied to have happened in the past.
4. To express courtesy in very formal situations set in the past.
5. In conditional sentences of type II to refer to the consequence of an unlikely condition in the past (si + imperfect subjunctive + conditional).
Some examples:
- Desearía que me comprendieras. (I wish you would understand me.)
- Dudaba que