This is a two-part question:
1) I have consulted multiple sources and found that 'it isn't' and 'it's not' have little to no semantic difference. If they are pretty much equivalent then for what reason is -
It's not like we didn't try our best
It isn't like we didn't try our best
If they are both correct grammatically why is the first construction much more common and even sound more natural. Is it a matter of placement of emphasis?
2) It is stated in a grammar article that tag question should be in the opposite form to the main question. However, in a case of two negatives yielding a positive like the example above, should the tag question be negation or positive?
- It's not like we didn't know what to do, is it?
- It's not like we didn't know what to do, isn't it?
Which one obeys the rule, 1 or 2?
Many thanks in advance.