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I understand contractions as just a means of merging two words into one, with some added punctuation, but there's some cases where I feel I'm grammatically correct, but using them incorrectly.
For example, "Have you ever been to the market downtown? I know I've."
Or, "Will you guys be coming with us?" ... "Yes we'll."
And, "If that won't work, what'll?"
Is there some grammar rule against doing this? Is there a reason why this isn't common? What makes doing this feel awkward?