The Subjunctive Mood is, used in conditional sentences to express an unreal condition (in the subordinate clause) and an unreal consequence (in the principal clause).

In sentences of unreal condition referring to the present or future the Past Subjunctive of the verb to be is used in the subordinate clause; with other verbs the same meaning is expressed by the Past Indefinite of the Indicative Mood. In the principal clause we find the analytical subjunctive consisting of the mood auxiliary should or would and the Indefinite Infinitive. Should is used with the first person singular and plural, would is used with the second and third persons singular and plural.

The world would be healthier if every chemist’s shop in England were demolished. (Shaw)
I should kill myself today if I didn’t believe that tyranny and injustice must end. (Galsworthy)

An unreal condition referring to the future can also be expressed by the Past Subjunctive of the verb to be + Infinitive of the notional verb or the analytical Subjunctive with the mood auxiliary should for all the persons.

If I were to offer my home… my station… my affections… to any one among the young women engaged in my calling, they would probably be accepted. Even readily accepted. (Dickens)
Well, Major, if you should send me to a difficult spot — with this man alone, I’d feel secure. (Heym)

If in the subordinate clause the mood auxiliary should is used, we often find the Indicative or Imperative Mood in the principal clause.

If any of your family should come to my house, I shall be delighted to welcome them… (Trollope)
If he should come, ask him to wait.

In sentences of unreal condition referring to the past the Past Perfect of the Indicative Mood is used in the subordinate clause; in the principal clause we find the analytical subjunctive consisting of the mood auxiliary should (with the first person) or would (with the second and third persons) and the Perfect Infinitive.

If I had consulted my own interests, I should never have come here.(Glsworthy)

There are two mixed types of sentences of unreal condition. In the first of these the condition refers to the past and the consequence refers to the present or future.

If you had taken your medicine yesterday, you would be well now.
No, by my word and truth, I never despised you; if I had I should not love you now! (Hardy)

In the second type the condition refers to no particular time and the consequence to the past.

If he were not so absent-minded, he would not have mistaken you for your sister.
Still Beatrice had taken the trouble to go up to London and to buy the books for me. She would not have done that if she disliked me. (Du Marnier)

Unreal conditions may also be expressed in the following ways:

But for the rain, we should go down to the country.
His fleshless face would have looked like the face of a mummy, but for the restless brightness of his little black eyes. (Collins)

If it were not for your help, I should not be able to finish my work in time.

If it hadn’t been for me, his own brother would have shut him up for life. If it hadn’t been for me, his own brother would have shut him up for life. (Dickens)

In sentences of unreal condition the modal verbs might and could are often used; they fully retain their modal meaning and therefore they do not form the analytical subjunctive.

Here we have the group ‘modal verb + Infinitive’ which forms a compound verbal modal predicate, whereas the analytical subjunctive forms a simple predicate.

If she were still waiting, she might be restless, feverish, but surely she would not look like this. (Galsworthy)
I could have done very well if I had been without the Murdstones. (Dickens)

Would, when used in the subordinate clause of a sentence of unreal condition, is also a modal verb forming with the infinitive a compound verbal modal predicate.

If you would come and see us… mother would be as proud of your company as I should be. (Dickens)

In conditional sentences of real condition naturally the Indicative and not the Subjunctive Mood is used. Such sentences can refer to the present, future or past.

But I can bear anything gladly if you are happy. (Eliot)
If you make this disgusting match, you will never see Hector again. (Shaw)
The whole thing was on his conscience — for if Jon had anything, he had a conscience. (Galsworthy)

The conjunctions introducing adverbial clauses of condition are: if, in case, provided, suppose, unless and some others. If is the most common conjunction used in sentences of real and unreal condition. In case and provided are chiefly used in sentences of real condition.

In case I don’t find her at home, I shall leave her a note.
I shall go there provided you consent to accompany me. (Ch. Bronte)

Suppose is more common in sentences of unreal condition.

Suppose he wrote to you, would you answer?

Unless is used in sentences of real and unreal condition.

I shall come in time unless I am detained at the Institute.
Isabel would not have engaged herself to Mr. Hardyman unless she had been fond of him. (Collins)

Adverbial clauses of condition containing the verbs had, were, could and should are often introduced without any conjunction. In these cases we find inversion.

Had the wanderer remained awake for another half-hour, a strange sight would have met his eyes. (Conan Doyle)
I should be myself were I once again among the heather in those hills.(E. Bronte)
Mary would indeed have been grateful, to Miss Dunstable, could she have known all that lady did for her. (Trollope)
Should he come this way, I will speak to him. (Ch. Bronte)

The Subjunctive Mood is used in sentences expressing what may be understood as an unreal consequence, the condition of which is not expressed as such.

I suppose you are a stranger in these parts, or you would have heard what happened last autumn. (Ch. Bronte)
There was no piano… because it would have taken up much room. (Galsworthy)