Why aren't vacuous truths just undefined? I am struggling to understand this. According to truth tables, if $P$ is false, it doesn't matter whether $Q$ is true or not: Either way, $P \implies Q$ is true.
Usually when I see examples of this people make up some crazy premise for $P$ as a way of showing that $Q$ can be true or false when $P$ is something outrageous and obviously untrue, such as "If the moon is made of bacon-wrapped apple-monkey carburetors, then I am a better wakeborder than Gauss."
$P$ is clearly false, but $P \implies Q$ is true no matter what the state of $Q$ is, and I don't understand why.
Are we saying "If $P$ is false, then all bets are off and $Q$ can be anything, either true or false, and not contradict our earlier claim, and if it isn't false, it must be true"?
Otherwise why can't we say that if $P$ is false, then we can't make any claims one way or the other on whether or not it implies anything at all? 

Intuitively, consider $P \implies Q$ to be a promise. For example: I say, "If you ever jump over the moon, then I'll pay you a thousand dollars." 
Now, some time passes and you obviously haven't jumped over the moon. The question is now effectively: Have I kept my promise true, or broken it (been false)? 
It seems clear that I've kept that particular promise, granted that at no time was I obligated to give you the thousand dollars. In fact, even if I had given you a thousand dollars for some other service, it wouldn't have any bearing on that particular, empty offer. 
