The Verb Phrase In Subordinate Clauses

Tenses, aspects and modal auxiliaries apply both subordinate and independent clauses. But there are cases in which choices affecting the verb phrase of a subordinate clause. With temporal since clauses it is the choice of verb phrase in the matrix clause that is affected. Subordinate clause prevents that clause from constituting in an independent sentence.

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The present tense adverbial and nominal clauses: The simple present is commonly used in preference to the auxiliary will or shall in certain types of adverbial clauses to express future meaning:
When he arrives the band will play the National Anthem. The subordinators belong to the temporal, conditional, and conditional connessive categories. SINCE is excluded. Clauses of similarity and proportion can also have the simple pres. to express future meaning. Next time I’ll do as she says.
Nominal that and wh-clauses contain simple pres. when the matrix clause refers to the future. That is what he will want tomorrow. There are exceptions after  which the simple present is regularly used: hope, bet see, take care, suppose and assume. Suppose he loses his way. Will and won’t can occur in adverbial, if clauses. The simple present refers to an assumed future actual situation. Modals refer to the assumed predictability of a situation. Will and wont are commonly used
1. where modals have volitional meaning: If you’ll use it, you can have it. Here simple present would suppress the volitional meaning.
2. Where the modals express timeless and habitual prediction: If drugs will cure him, this drug will do the job.
3.
Modals express the present predictability of the occurence or nonoccurence of a future situation: If you wont arrive before six, I cant meet you. Matrix clause expresses the present consequence of the present predictability. Modals can be replaced by the simple present but with a different implication.

The hypothetical past and the past perfective: The verbs in hypothetical clauses are backshifted,
the past tense form form being used for present and future time reference and the past perf. for past time reference. Hypothetical past and perfective. The most commonly used modal in the matrix clause is WOULD. It expresses the hypothetical implication. The hypothetical meaning is more absolute in the past with present and future reference the meaning can be negative expectation or assumption. Modals in hypothetical conditional clauses combine with past and past perf. In the matrix clause they raplace WOULD. Modals in hypo. conditions apart from the hyp. would are could, would, might should. If they would help us we could finish early. In certain other constructions that have hypo. meaning hypo. past or past perf. are obligatory. It’s time you were in bed. Can express negative implication or hypo. past may express tentative politeness.I’d rather we had dinner now.

The present and past subjunctive:
Used very occasionally in formal style, open conditional clauses, and in concessive clauses. If any person be found guilty, he shall have the right of appeal. More usually the simple pres. indicative is used. Clauses of concession and purpose express putative rather than factual meaning: Though he be the president himself, he shall hear us. More usual for the though clause are the simple pres. indicative or putaive should followed by the infinitive. In that clauses after verbs, adjectives, the present subjunctive is used. Congress has voted that the present law be maintained. Mandative subjunctive is used when the matrix verb is past. Putative SHOULD with the infinitive is far more common. The past subjunctive is used in formal style in hypo. conditional clauses and in other constructions with hypo. meaning. I wish she were not married. In formal style we use WERE.

Putative should:
Used in that clauses to convey the notion of  a putative situation which is recognized as possibly existing or coming into existence. Nonfactuality. The should construction has nonfactual bias. In that clauses when the matrix contain verbs adjectives or nouns that convey an emotional reaction or that express a necessity, plan, or intention for the future we use putative SHOULD. It is replaceable by infinitive clauses or present subjunctive. A past verb in the matrix clause do not necessarily affect the form of should in the subordinate clause.

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The perfective with temporal clauses:  With temporal since clauses: The temporal since clause generally requires the present perf. in the matrix clause when we refer to the stretch of time up to the present.: I have lost ten ponds since I started swimming. When the clause contains a prepositional phrase introduced by since or the prepositional adverb since. In informal lang. nonperfective forms are commonly used in matrix clauses with since clauses. There are some exceptions to the general rule for matrix clauses. In most cases both perf and nonperf forms are possible.
1. When the predication is durative statively used verbs (be,seem) may take nonperf forms. It’s Ok since I had it fixed. The most common pattern is IT+BE+ a time expression in which the verb is in simpl past, or simpl. pres. or have the will future. Nonperfective forms are normal here. Other verbs (seem) also fit into this pattern. It seems a long time since we last met. Perfective forms may also be used.  
2.
Modal auxiliaries (can,could) or semi-aux. occur in the matrix clause in nonperfective forms. Modals can not be used here in perfective forms. Perfective modals may be used when the matrix clause refers to a situation in the past.
3.
The simple present or the pres. progr. is sometimes used in the matrix clause when that clause has habitual reference. When the whole period under consideration is distanced in past time, the past. perf. is generally used in the matrix clause.  The past perfective may be replaced py the simple past.  A past modal perfective is used in the matrix clause when the period in time matrix clause refers to a future time in the past. Since clause: Simple past is used when the clause refers to a point of time, marking the begining of a situation, referred to in the matrix clause. Present perfective is used when the clause refers to a period of time lasting to the present. Pres. perf. may also be used in the pattern it+be+time expression, when there is no explicit indication of point of time. When the period is placed in past time the past perf. or the simple past is used.

The perfective with other temporal clauses: When an after clause refers to a past event the varb may be in the past perf. or in simple past. In case of when it is the same. WHEN suggests that one action follows immediately the other. If the sequence of events is habitual the werb in aft or when clause may be in the pres. perf. Also when there is a repetitiveness of the situation and in temporal and conditional clauses for a future event that precedes the future event referred to in the matrix clause. In case of before we use past perf. Nonfactual. The event in a before clause may not have taken place.