(from "Index to Modern English" by Thomas Lee Crowell Jr.)
Sequence of tense:
1. The two sentences below mean the same thing, but notice the difference in the verb forms:
Today's paper
says that it
will rain tomorrow if it
does not snow.
Today's paper
said that it
would rain tomorrow if it
did not snow.
2. In general, the tense form of a dependent verb is determined by the tense of the principal verb: the dependent verb shows time
in relation to the principal verb. The phenomenon is known as
sequence of tense. It is found to varying extent in other languages, but it permeates English so throughly that it may be termed a distinctive characteristic of English. It appears not only in dependent clauses but also in infinitives and participles.
Notice the operation of sequence of tense in the following models:
Model 1
a. She knows that John loves her. (The time of the dependent verb
loves is the same as that of the principal verb
knows.)
b. She knows that John will love her. (The time of the dependent verb combination
will love is later than (or subsequent to or future to) that of the principal verb
knows.)
c. She knows that John loved her. (The time of the dependent verb
loved is earlier than - or anterior to - that of the principal verb
knows.)
Model 2
a. She knew that John loved her. (The time of the dependent verb
loved is the same as that of the principal verb
knew.)
b. She knew that John would love her. (The time of the dependent verb combination
would love is future to that of the principal verb
knew.)
c. She knew that John had loved her. (The time of the dependent verb combination
had loved is earlier than that of the principal verb
knew.)
Model 2 is so firmly entrenched in English that a general rule can be set up:
if the principal verb is in the past, the verb in the dependent clause is also in the past.
You may see some violations of that general rule. Sometimes, if the dependent clause states a general truth, describes a habitual action, or expresses a permanent condition, the simple present tense is used in violation of the rule of sequence of tense. However, the sequential form is just as correct and is more usual, and it is recommended that all speakers use it.
- Columbus proved that the world
was round.
- The visitor discovered that the subway train always
stopped at 96th Street.
- The teacher asked me what my name
was. (I didn't change my name, did I?
)
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