1. SEQUENCE(S) OF TENSES
Let's recall: a complex sentence is one with at least one main clause and at least one subordinate clause. It might have more than one of either or of each.
Now, the actions or events in these clauses don't necessarily happen at the same time. For example, "Because you studied hard last night, you will do well on the quiz today."
The main (or leading) clause, "you will do well on the quiz today," is future, but the subordinate, causal, clause, "Because you studied hard last night," is past.
The relationship between the tense of a subordinate and that of its main (or leading) clause’s verb is called Sequence of Tenses, in Latin consecutio temporum, a term from the Middle Ages, not from ancient Rome.

2. In this unit we'll be concerned with this tense-relationship only when a subordinate clause's verb is in the subjunctive mood.
But remember that many kinds of subordinate clauses can or even must have an indicative verb.
Remember, too, that subordinate and subjunctive are not the same thing!
We’ll study only subjunctive subordinate clause verbs for two reasons:
because the subjunctive lacks the future and future perfect
and because the tenses of the subjunctive mood don't express the times of actions in the fixed way that the indicative does.

3. The tense of a subjunctive subordinate clause verb depends on a Latin author's need to represent an event or action as occurring
before,
at the same time as, or
after
the action or event related by the introductory, "super-ordinate" verb of the clause or phrase on which the sub-ordinate clause depends.
In Latin, when a dependent verb is subjunctive, the time-relationship of tenses follows a general pattern, shown in the table on the next slide. The top row is usually referred to as the "primary" or "present" sequence and the bottom row the "secondary" or "historical" sequence. This is a general principle, not a hard and fast rule!

4. introductory clause verb
before
same time as
after
Present
Future
Present & Future Imperative
Future Perfect
Present Perfect ("have," "has")
Historical Present
PERFECT
SUBJUNCTIVE
PRESENT SUBJUNCTIVE
FUTURE PERIPHRASTIC
(FUTURE ACTIVE PARTICIPLE + PRES. SUBJ. of esse)
Imperfect
Historical Infinitive
Historical Perfect (simple past)
Pluperfect (“had”)
PLUPERFECT
IMPERFECT SUBJUNCTIVE
(FUTURE ACTIVE PARTICIPLE + IMPERF. SUBJ. of esse)

5. indirect questions show the fullest range of possibilities for these sequences. Here are two examples. The first has a present-tense leading verb (sciō) and demonstrates the primary sequence, while the second has an imperfect leading verb (sciēbam) and demonstrates the secondary sequence:
before
same time as
after
sciō
I know (now)
quid
what
ēgeris
you did
you have done
you were doing
agās
you are doing
actūrus sīs
you are going to do
you will do
sciēbam
I knew (then)
ēgissēs
you had done
agerēs
actūrus essēs
you were going to do
you would do

6. introductory clause verb
Remember: that's a general rule.
In fact, different subordinate clause types have their own tense relationships with their leading (“super-ordinate”) clause verbs. Here are examples of the major types.
PURPOSE CLAUSES (including noun purpose or "indirect command" clauses):
introductory clause verb
after
Present
Future
Present & Future Imperative
Future Perfect
Present Perfect ("have," "has")
Historical Present
PRESENT SUBJUNCTIVE
Imperfect
Historical Infinitive
Historical Perfect (simple past)
Pluperfect (“had”)
IMPERFECT SUBJUNCTIVE

7. Tense sequence in purpose clauses
Let’s think about it: a purpose is some desired outcome.
That means that a clause expressing a purpose will always stand in a “future” or “after” relationship to a leading clause. Purpose clauses can’t show “before” or “at the same time” relationships.
edimus ut vīvāmus, we eat (in order) to live, i. e. we eat so that we might, in the near future, continue to live. Here the present subjunctive represents a future state.
Orgetorix suae civitati persuasit ut de finibus suis exirent, Orgetorix persuaded his tribe to leave their own territory.
The indicative imperfect is always a past tense; but an imperfect subjunctive purpose clause verb represents a future action relative to the time of the leading clause’s verb.

8. introductory clause verb
RESULT CLAUSES (including noun or substantive result clauses, either as subject or object):
introductory clause verb
same time or after
Present
Future
Present & Future Imperative
Future Perfect
Present Perfect ("have," "has")
Historical Present
PRESENT SUBJUNCTIVE
Imperfect
Historical Infinitive
Historical Perfect (simple past)
Pluperfect (“had”)
IMPERFECT SUBJUNCTIVE

9. Tense sequence in result clauses
Result clauses can’t represent action before a leading verb, because, by definition, a result is a following consequence; it must occur either at the same time as or after another action or state. Consider these examples:
Cucurrit tantā celeritate ut mox ad urbem pervenerit, He ran with such speed that he soon reached the city.
Accidit eā nocte ut lūna esset plēna, “It” happened that night that the moon was full. Did the “happening” occur after the full moon? No, they’re the same action.
Caesar effēcit ut milites pontem facerent, Caesar brought “it” about that the soldiers built a bridge.
Erat tam benignus ut omnes eum amarent, He was so kind that everyone loved him.