Adverbial clauses of this type contain some condition (either real or unreal) which makes the action in the main clause possible.
Adverbial clauses of condition may be introduced by conjunctions: if, unless, once, in case. There are also several conjunctions derived from verbal forms sometimes followed by the optional that: provided (that), providing (that), suppose (that), supposing (that), considering (that), given (that), granted (that), granting (that), admitting (that), presuming (that), seeing (that).
Conditional clauses introduced by if and other conjunctions (with the exception of unless) imply uncertainty. Therefore they often contain non-assertive forms of pronouns and pronominal adverbs, such as any, anybody, anything, anywhere.
If anything troubles you, you’d better tell me.
If anyone asks for me, tell him to wait.
Clauses beginning with unless express the only possible condition which will make the action in the main clause possible. Therefore they usually contain assertive forms like something, somebody.
Unless somebody interferes, there may be a disaster.
For the same reason unless-clauses hardly ever express unreal conditions.
The exclusive meaning of unless accounts for the fact that, even if the condition is real, the unless-clause is not always equivalent to an if-not-clause. Thus the sentence: I won’t come unless you invite me (я приду, только если вы пригласите меня) and the sentence I won’t come if you don’t invite me (= я не приду, если вы меня не приглашаете) are quite different in their meaning.
The conjunction provided opens a clause containing some desirable condition for the fullfilment of the action expressed by the predicate in the main clause.
And you can do what you please, provided you do it neatly and don’t make a row over it.
The conjunctions suppose and supposing always imply that the condition is merely hypothetical.
I mean this: Suppose some other European pauper prince was anxious to marry Princess Anna and her
fortune, wouldn’t that Prince have an interest in stopping this loan of yours to Prince Eugen?
Conditional clauses may be joined to the main clause asyndetically by means of link-inversion. Inversion is possible only if the predicate in the subordinate clause is in the subjunctive mood, that is expressed by past subjunctive (were), or by non-factual Past Perfect.
But had chance taken you out into the surrounding country and had it taken you in the right direction,
you would have found him toiling along by the hedges...
§ 170. Depending on the relation between the subordinate and the main clauses and on the use of tense and mood forms, complex sentences with conditional clauses may be subdivided into three types:
I.Complex sentences with clauses of real condition are those when the actions or events in both the clauses refer to the past or present and these actions or events are regarded as real facts. If the actions or events in these clauses refer to the future, the actions or events are regarded as possible real facts.
If I have offended you, I am very sorry.
Why did he send us matches if he knew there was no gas?
If Jules comes back, simply defy him to enter - that is all.
I won’t phone you, unless something unforeseen happens.
The conditional clause may be a statement for mere argument, no condition is meant.
If she got no money from her brother-in-law, she got what was as good as money - credit.
If Adrian had a passion, indeed, except for Diana Ferse, it was a burning desire to fix that breeding spot,
As can be seen from the above examples, the predicates in conditional clauses may be in the past or present indefinite, present perfect, present or past continuous.
Note:
In cases like the following Let her come to me as she will, when she will, not at all if she will not; But I must run out for half a minute, if you’ll let me the verb will is not auxiliary but modal, as it expresses wish, insistence, or resistance (in negative form).
II.Complex sentences with clauses of open condition. These clauses denote hypothetical situations or circumstances which may be (or may not be) realised in the present or future. Accordingly the subjunctive-mood forms are used both in the subordinate and the principal clause to denote actions or states.
| In the main dause | In the subordinate clause | |||
| 1. | Analytical forms with | 1. | The present subjunctive (be, go, see, etc.) or the past subjunctive for all the persons in the singular and plural. Of these forms be and were can open asyndetically joined clauses. | |
| should + would | non-perfect infinitive | |||
| (in Modern English the tendency is to use would for all the persons) | ||||
In case the state of the patient became worse he would be taken to a hospital.
If I were you, I would change into another dress.
You wouldn’t be talking that way unless you were hurt.
| 2. | Quasi-subjunctive-mood forms with may (might) + non-perfect infinitive | 2. | The non-factual past indefinite and past continuous. |
You might ask her this question if you were less scrupulous.
This might seem to be unreal unless I saw it with my own eyes.
| 3. | The imperative mood. | 3. | Analytical forms with should + non-perfect infinitive (mostly with inversion). |
Should he ask for references, tell him to apply to me.
Note:
The form would + infinitive in the subordinate clause may be not a mood form, but a compound predicate, expressing a polite request.
I should be much obliged if you would agree to take part in the concert (если бы вы согласились
участвовать в концерте).
III.Complex sentences with clauses of rejected condition imply non-fulfilment of the condition, as the actions or events described in the conditional clause refer to the past and the time of their realization is over. The condition is generally not even supposed to have been fulfilled, but is stated merely for the sake of argument. The following mood forms are used;
 In the main clause analytical forms | In the subordinate clause non-factual past perfect | |
| should would might (may) could | + perfect infinitive | |
If I hadn’t woken you, you’d (would) have lain there for the whole fortnight.
She would have been playing her part well unless she had been stiff with fright.
I might have persuaded her to change her mind if she had not been so obstinate.
If the book had been published they could have bought a copy in the shops.
Could he not have missed the train if he had been detained by the director?*
* The forms with may (might) and could are compound verbal modal predicates in the subjunctive mood.
The non-factual past perfect form may open an asyndetically joined conditional clause (with partial inversion).
Had the colour of the dress been to my taste, I should have bought it.
Had the world been watching, it would have been startled.
§ 171. A complex sentence with a conditional clause may be built on clauses of both type II and III, thus forming a mixed type of conditional relationship. For instance:
If we hadn’t been such fools, we would all still be together. (the subordinate clause with reference to the
past - type III, the principal clause with reference to the present - type II).
If you were more attentive, you would’t have made so many mistakes (the subordinate clause with
reference to the present, as it implies somebody's ability to concentrate in general - type II, the main
clause with reference to the past - type III).
Note:
Some of the conditional constructions may be used to join clauses expressing other meanings or admitting a two-fold interpretation. Thus if may introduce concessive clauses (see § 172), clauses in which the meaning of condition is combined with temporal meaning. The conjunction in case may introduce clauses of negative purpose, as in:
I went and ate sandwiches in the woods, in case one of the servants should see me on the lawn from the
window... (чтобы кто-нибудь из слуг не увидел...)