1. Sequence of Tenses

2. I. What is sequence of tenses?
Sequence of tenses in its narrow sense refers to principles according to which the tenses of subordinate clauses are suited to the tenses of principal clauses.
Sequence of tenses in its broad sense refers to principles according to which tenses in any discourse are suited to each other.

3. II. What are the principles?
1.1 The principal-determining-subordinate principle, which means that the tense form of the principle clause determines the tense form of the subordinate clause
1.2 The back-shift principle, which means that, when the direct speech is transformed into the indirect speech, the tense in the direct speech is back-shifted after a past tense reporting verb

4. Note
The two principles above are by nature grammatical-concord principles, which take into account some superficial factors but fail to reveal the nature that underlies these factors, and, as a result, fail to fully account for the language phenomena involving sequence of tenses.

5. Compare the Following:
(1) a. The philosopher said, “Everything has
two sides.”
b. The philosopher said that everything
has/had two sides.
(2) a. She said, “I wish I were a boy.”
b. She said she wished she were/? had been a boy.

6. (3) original reported
I see he saw
I saw
I have seen he had seen
I had seen

7. 1.3 The notional-concord principle, which requires that the time relationship between the action state and its reference time in the indirect speech remain the same as that in the direct speech. This principle agrees with the law of cognition and the way of thinking in using tenses and reveals the nature of the sequence of tenses of English. So it is the principle that governs the sequence of tenses.

8. 1.3.1 Sequence of tenses is the normal use of tenses.
(1) a. He told us that he finished/had finished his work the
proceeding week.（priority）
b. He told us that he was having a holiday then.
（simultaneity）
c. He told us that he would start work again in a few days.
（posteriority）
(2) a. She says she was not very well yesterday.（priority）
b. She says she is feeling much better now.
c. She says she will be well again very soon.（posteriority）

9. 1.3.2 Transformation of the direct speech into the indirect speech is by nature the shift of the reference time.
The present tense is back-shifted if the reference time is shifted.
(1) a. “( ) I have experienced such difficulties
before.”（priority）
b. Jack told me that he had experienced such
difficulties before.（priority）
(2) a. “( ) I’m trying to make what is impossible
possible.”（simultaneity）
b. Mary said she was trying to make what was
impossible possible.（simultaneity）

10. 1.3.2.2 The present tense is not back-shifted if the reference time is not shifted.
a. Copernicus concluded, “The earth goes
round the sun.”
b. ( ) Copernicus concluded that the earth
goes round the sun. (simultaneity)
c. Copernicus concluded that the earth went
round the sun. (simultaneity)

11. The past tense is not back-shifted if the time relationship is clear and no ambiguity arises.
(1) a. Ann explained, “The exhibition finished last week.”
b. Ann explained that the exhibition finished/had finished
the previous week.
(2) a. Mary said, “When I saw him last he was playing
tennis.”
b. Mary said that when she saw him last he was playing
/had been playing tennis.
(3) a. He said, “We hadn’t returned to the store when she
came.”
b. He said they hadn’t returned to the store when she
came.

12. 1.3.2.4 The past tense is back-shifted if the time relationship is not clear and ambiguity arises.
(1) a. “( ) I was married (, but my husband died last year).”
（priority）
b. She said that she had been married/*was married.
c. “( ) I was married in the church.” (priority)
d. She said that she was married/had been married in
the church. (priority)
(2) a. “( ) I was living in the United States then.”（priority)
b. He told us that he had been living in the United States
then.（priority）
c. He told us that he was living in the United States then.
（priority/simultaneity）

13. 1.3.2.5 The past tense is not back-shifted if the time relationship is hypothetical.
(1) a. “( ) If I had received the invitation, I would
have come.”（priority）
b. He said that if he had received the invitation,
he would have come.（priority）
(2) a. “I wish I had wings.”（simultaneity）
b. Thomas said he wished he had wings.（simultaneity）
(3) a. “( ) She is screaming as if she would die in minute.”
(posteriority)
b. He said she was screaming as if she would die in a minute. (posteriority)