Rules for the change of tenses in subordinate clauses

If the subordinate clause is an adjective clause, it can be in any tense.

Study the examples given below.

• Yesterday I met a man who sells hats. (Here the principal verb is in the past tense, but the verb in subordinate adjective clause is in the present tense.)
• Yesterday I met a man who sold me a hat. (Now the verbs in the principal clause and the subordinate clause are in the past tense.)
• Yesterday I met a man who will one day sell me a hat. (Now the verb in the principal clause is in the past tense whereas the verb in the subordinate clause is in the future tense.)

When the subordinate clause is introduced by a conjunction of purpose

Use may in the subordinate clause when the verb in the principal clause is in the present tense or the future tense. Use might in the subordinate clause when the verb in the principal clause is in the past tense.

• We eat that we may live.
• I worked that I might pass.
• I will work that I may pass.

After expressions like if only, as if, it’s time and wish that

A past tense is used after expressions like if only, as if, it’s time and wish that.

• I wish that she would come. (NOT I wish that she will come.)
• It is time they went to bed. (NOT It is time they go to bed.)

A past tense used after as if indicates that the statement is not true.

• He talks as if he were mad. (But he is not mad.)
• He talks as if he is mad. (He may be mad, but we don’t know.)