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English definition of “when”


adverb, conjunction     /wen/
A1 at what time ; at the time at which: "I did tell you about it." "When? I don't remember ." When are you going? When's the baby due ? We'll go when you're ready . Tell me when to start . Ask him when he's next coming home . When do you expect to have the project completed (by)? She was only 20 when she had her first baby . He was quite shocked when I told him. I hate it when there's no one in the office . I went there when I was a child . I was just getting into the bath when the phone rang .Question words and expressions Grammar:As, when or while?As, when and while are conjunctions. In some uses as, when and while can mean the same, but they can also have slightly different meanings. We use them to introduce subordinate clauses.Grammar:AsWe can use as to introduce two events happening at the same time. After as, we can use a simple or continuous form of the verb. The continous form emphasises an action that interrupts or occurs during the progress of another action:Grammar:WhenWe can use when to introduce a single completed event that takes place in the middle of a longer activity or event. In these cases, we usually use a continuous verb in the main clause to describe the background event:Grammar:While and asWe can use while or as to talk about two longer events or activities happening at the same time. We can use either simple or continuous verb forms:Grammar:When and while without a subjectWe can use when and while without a verb, or without a subject + auxiliary verb be:Grammar:If or when?We use if to introduce a possible or unreal situation or condition. We use when to refer to the time of a future situation or condition that we are certain of:Grammar:Relative pronouns: when, where and whyIn informal language, we often use where, when or why to introduce defining relative clauses instead of at which, on which or for which.Grammar:WhenWhen is a wh-word. We use when to ask questions, as a conjunction and to introduce relative clauses.Grammar:When as a question wordWe can use when to ask for information about what time something happens:Grammar:When as a conjunctionWe use when as a conjunction meaning ‘at the time that’. The clause with when is a subordinate clause (sc) and needs a main clause (mc) to complete its meaning. If the when-clause comes before the main clause, we use a comma.Grammar:When as a relative pronounWe can use when as a relative pronoun in relative clauses:Grammar:Since when?We can use since when to ask at what time something began. We often use it as a response when we are surprised that something has begun:Grammar:When or if?We use when to refer to a future situation or condition that we are certain of, whereas we use if to introduce a possible or unreal situation.Grammar:When or since?We use when to mean ‘(at) the time that’. We use since to refer to a particular time in the past until another time or until now:Grammar:When: typical errors
(Definition of when adverbconjunction from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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