Yes.....'At one time people would have found the idea of a spherical Earth completely illogical.'......that's it...Period! Now...don't immediately say 'it is not illogical' as though logic is something Absolute
Logic is an absolute. Sorry, but you are wrong.
Logic is not absolute. It is relative and connected to our current understanding.
Wrong. How we apply logic to the real world is connected to our understanding of it, but logic itself is absolute.
Philosophers talk about two properties of logical arguments:
An argument is logically valid if it is internally consistent. To take an example from Wikipedia
1 All organisms with wings can fly.
2 Penguins have wings.
Therefore,
3 penguins can fly
This is a logically valid argument. If the premises are true (1 and 2), the conclusion (3) is also true. Your understanding of penguins, wings and flying are irrelevant, the argument is logically valid.
An argument is sound if is valid and its premises are true. Clearly, the above argument is not sound because premise number 1 is false. However, just because we know premise number 1 is false doesn't mean the logic is wrong.