If conditions

Indicative: If it is raining in New York, then Mary is at home.
Counterfactual: If it was raining in New York, then Mary would be at home.
In older dialects and more formal registers, the form "were" is often used instead of "was". Counterfactuals of this sort are sometimes referred to as were'd up conditionals.^[2]
Were'd up: If I were king, I could have you thrown in the dungeon.
The form "were" can also be used with an infinitive to form a future less vivid conditional.^[3]
Future Less Vivid: If I were to be king, I could have you thrown in the dungeon.
Counterfactuals can also use the pluperfect instead of the past tense.
Conditional perfect: If you had called me, I would have come.
English language teaching[edit]
In English language teaching, conditional sentences are often classified under the headings zero conditional, first conditional (or conditional I), second conditional (or conditional II), third conditional (or conditional III) and mixed conditional, according to the grammatical pattern followed, particularly in terms of the verb tenses and auxiliaries used.
Zero conditional[edit]
"Zero conditional" refers to conditional sentences that express a factual implication, rather than describing a hypothetical situation or potential future circumstance (see Types of conditional sentence). The term is used particularly when both clauses are in the present tense; however such sentences can be formulated with a variety of tenses/moods, as appropriate to the situation:
If you don't eat for a long time, you become hungry.
If the alarm goes off, there's a fire somewhere in the building.
If you are going to sit an exam tomorrow, go to bed early tonight!
If aspirins will cure it, I'll take a couple tonight.
If you make a mistake, someone lets you know.
The first of these sentences is a basic zero conditional with both clauses in the present tense. The fourth is an example of the use of will in a condition clause^[4] (for more such cases, see below). The use of verb tenses, moods and aspects in the parts of such sentences follows general principles, as described in Uses of English verb forms.
Occasionally, mainly in a formal and somewhat archaic style, a subjunctive is used in the zero-conditional condition clause (as in "If the prisoner be held for more than five days, ...). For more details see English subjunctive. (See also § Inversion in condition clauses below.)