If I can tell a story in which A exists and B doesn't exist,

如果我跟你说A存在但B不存在
it's got to follow that A and B are not the same thing.

就可以得出结论A和B不是一个东西
Because if B was just another word for,

因为如果B只是
another way of talking about, A,

A的另一种表达方式
then to imagine A existing but

那么认为A存在而
B not existing would be imagining A existing but--

B不存在就是认为A存在但
well, B is just A--A not existing.

B 也就是A 却不存在
But of course,

显然
you can't imagine a world in which A exists but A doesn't exist.

你无法想象一个A既存在又不存在的世界
Put the same point the other way around:

把这点推而广之
If I can imagine A without B,

如果我可以想象A在没有B的情况下存在
then A and B have to be logically distinct things.

那么A和B在逻辑上是相互独立的