If + subjectThe person or thing that performs the action of a verb or that is described by a verb. E.g.: Andy has never been to Brunei. ("Andy") + auxiliaryA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am") can be replaced in formalNot belonging to colloquial or everyday speech; official. E.g.: I demand that Mr Smith call the person on whom the committee has decided. English, or for dramatic effect, by the inversionA structure in which a verb or an auxiliary precedes the subject. E.g.: "Here comes the sun." of the auxiliary and the subject, with the if omitted.

Will you sit down? (= If you will sit down…)
Should you need anything... (= If you should need anything...)
Were I in his shoes... (= If I were in his shoes...)
Were I to tell you… (= If I were to tell you…)
Could you tell me where the station is? (= If you could tell me where the station is…)
Would you come in, please? (= If you would come in, please.)
Had I known... (= If I had known...)
Had it not been for your foolishness... (= If it hadn’t been for your foolishness...)

Less likely conditions in third conditional
IF-sentences and conditionals Notes: IF-sentences and conditionals