no verb agreement
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He swims but He can swim.
*He cans swim.
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never followed by to
or a verb with -ing or -ed/-en
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I want to swim, I am
swimming, I have swum but
I can swim, *I can to swim,
*I can swimming, *I can swum.
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can not follow to have -ing or -ed/-en ending
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*I want to can swim. *To
can swim is wonderful. *After canning swim, he went home. *He is
canning swim. *He has canned swim.
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can not be used with do
to form questions or negatives
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He does not swim. Does he
swim? but
*He does not can swim. *Does he can swim?
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the past tense form
usually signals present or future activity rather than past
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He might swim this
afternoon. *He might swim yesterday.
He should swim this afternoon. *He should swim yesterday.
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are always the first
auxiliary before the verb. Can not be combined with another modal.
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He may have been
swimming. *He have may been swimming.
*He may can swim. *He might could do it.
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