Videos
For example, "I've never met my parents; I have no idea who they're."
or
Is anyone else hungry? Because we're.
Obviously, those are both terrible sentences, but if they're=they are and we're=we are, shouldn't it work?
‘An A-Z of English Grammar and Usage’ by Leech and others suggests the following:
With be, use the contraction + not (e.g. That’s not right).
With have and modal auxiliaries, use the verb + n’t option, e.g. hasn’t, can’t.
The authors go on to say that forms such as She isn’t hungry, as opposed to She’s not hungry, are less common, and that forms such as I’ve not met him, as opposed to I haven’t met him, are much less common.
The authors don’t say on what basis they make their recommendations, but they are likely to be based on frequency of use. There doesn’t seem to be any difference of meaning or emphasis. I would just add myself that a contraction such as I’ve not met him sounds more formal, perhaps because of its lower frequency.
As you've said, placing emphasis on a word is a matter of desired emphasis which is a matter of personal style rather than rules. I think you could make exactly the same point by putting stress on isn't (It ISN'T my fault!)
In the Python sketch, the emphasised word is 'it' not, 'not'. Part of the humour in the sketch is the repetition of it - 'It is.' 'No, it isn't.' 'Yes it is.'. This wouldn't have carried the same impact if the humour was based on, perhaps, the back and forth of 'It's not', 'Yes, it is.' 'No, it's not.'
Also, they can do this with a number of forms of the sentences in the sketch, for example 'It can be.' 'No, it can't ...' The humour wouldn't carry through these sentences if the emphasis had been used on the 'Is/Not' structure.
Both versions are correct, and both mean "The dog is not running."
Any difference in connotation is more likely to be expressed via context or tone than the placement of the contraction, in my opinion.
(For what it's worth, the dog's not doesn't technically contain a contraction of is not - it contains a contraction of dog is. But I don't think that's what you're asking.)
The contraction of "is not" is "isn't." "Ain't" is a slang form that is attributed to "is not," "are not," and "am not," and is considered substandard English.
The two sentences are identical in meaning, just different in the way that the verb is placed; both are grammatically correct. In the first, the verb is contracted with "not," and in the second, the verb is contracted with the subject. Both forms are considered informal English, and the second is discouraged for use in standard English writing.
If aren’t is a contraction for are not, why do we say things like aren’t you or aren’t I, etc…
Are not you and are not I aren’t grammatically correct so why do we say them all the time in every day language