English verb conjugation COULD HAPPEN

Regular verb: happen - happened - happened


Affirmation

Simple form

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it could happen
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V-ing form

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it could be happening
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Perfect

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it could have happened
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V-ing perfect

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it could have been happening
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Negation

Simple form

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it could not happen
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V-ing form

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it could not be happening
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Perfect

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it could not have happened
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V-ing perfect

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it could not have been happening
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Interrogative form

Simple form

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could it happen?
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V-ing form

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could it be happening?
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Perfect

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could it have happened?
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V-ing perfect

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could it have been happening?
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Interro-negative form

Simple form

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could it not happen?
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V-ing form

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could it not be happening?
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Perfect

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could it not have happened?
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V-ing perfect

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could it not have been happening?
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