The sequence of tenses (known in Latin as consecutio temporum, and also known as agreement of tenses, succession of tenses and tense harmony) is a set of grammatical rules of a particular language, governing the agreement between the tenses of verbs in related clauses or sentences. A hypothetical context in which rules of sequence of tenses apply is that of indirect speech. If, at some past time, someone spoke a sentence in a particular tense (say the present tense), and that act of speaking is now being reported, the tense used in the clause that corresponds to the words spoken may or may not be the same as the tense that was used by the original speaker. In some languages the tense tends to be "shifted back", so that what was originally spoken in the present tense is reported using the past tense (since what was in the present at the time of the original sentence is in the past relative to the time of reporting). English is one of the languages in which this often occurs. For example, if someone said "I need a drink", this may be reported in the form "She said she needed a drink", with the tense of the verb need changed from present to past. The "shifting back" of tense as described in the previous paragraph may be called backshifting or an attracted sequence of tenses. In languages and contexts where such a shift does not occur, there may be said by contrast to be a natural sequence.
English In English, an attracted sequence of tenses (backshifting) is often used in indirect speech and similar contexts. The attracted sequence can be summarized as follows: If the main verb of a sentence is in the past tense, then other verbs must also express a past viewpoint, except when a general truth is being expressed. For example, if Batman speaks the following words:
I need a special key for the Batmobile. the speech act may be reported using the following words:
Batman said that he needed a special key for the Batmobile. with the present tense need replaced by the past tense needed, since the main verb of saying (said) is in the past tense. Further examples can be found at Uses of English verb forms § Indirect speech. In some cases, though, a natural sequence of tenses is more appropriate. Here the tense of a verb in a subordinate clause is not determined by the tense of the verb in the superordinate clause, but is determined simply according to the sense of the clause taken apart from the rest of the sentence. The rule for writers following the natural sequence of tenses can be expressed as follows: imagine yourself at the point in time denoted by the main verb, and use the tense for the subordinate verb that you would have used at that time. Thus the tense used in the indirect speech remains the same as it was in the words as originally spoken. This is normal when the main verb is in the present or future tense (as opposed to past tense or conditional mood). For example:
Batman says that he needs a special key for the Batmobile. (main verb in present tense) Batman has said that he needs a special key for the Batmobile. (main verb in present perfect, not past tense, so no backshifting) However it is also possible to use the natural sequence even if the main verb is past or conditional:
Batman said that he needs a special key for the Batmobile. This option is more likely to be used when the circumstance being expressed remains equally true now as it did when the speech act took place, and especially if the person reporting the words agrees that they are true or valid. Debate amongst grammarians over the appropriateness of the two types of sequence of tenses goes back as far as the 18th century. Use of the attracted sequence sometimes leads to additional problems when the grammatical construction of indirect speech includes an incorporated quotation – that is, when an attempt is made (though using indirect rather than direct speech) to report the words actually spoken. For example, if a minister spoke the words "Such a policy is not without its drawbacks", then a writer may attempt to report this as follows:
The minister admitted that "such a policy is not without its drawbacks". using quotation marks to denote that that portion of the sentence represents the minister's actual words. This, however, requires use of the natural sequence of tenses, which might not be felt appropriate in the given situation. There are various possible solutions to this problem:
Rearrange the sentence so that the incorporated quotations become set off, possibly as direct speech: The minister did not claim perfection: "such a policy is not without its drawbacks", he admitted. Cut down the incorporated quotation to exclude the verb: The minister admitted that such a policy was "not without its drawbacks". Use square brackets to indicate where the words deviate from those actually spoken: The minister admitted that "such a policy [was] not without its drawbacks". Similar problems arise from the other changes that typically occur in indirect speech, such as changes of pronoun (depending on speaker). For more details, see the article on indirect speech, and also the article on uses of English verb forms, particularly the sections on indirect speech and dependent clauses.
Russian Indirect speech in Russian and other Slavic languages generally uses the natural sequence of tenses (there is no backshifting). For examples, see Indirect speech § Russian.
Latin
In Latin, the sequence of tenses rule affects dependent verbs in the subjunctive mood, mainly in indirect questions, indirect commands, and purpose clauses. If the main verb is in one of the non-past tenses, the subordinate verb is usually in the present or perfect subjunctive (primary sequence); if the main verb is in one of the past tenses, the subordinate verb is usually in the imperfect or pluperfect subjunctive (historic sequence). For example, when the subordinate verb refers to a time contemporaneous or later than the time of the main verb, the present or imperfect subjunctive is used:
quaerit ubi sit (present subjunctive) 'he asks where it is' quaesivit ubi esset (imperfect subjunctive) 'he asked where it was' When the subordinate verb refers to a time earlier than that of the main verb, the perfect or pluperfect subjunctive is used:
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