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If -1 - 1 = 0 then tomorrow is Thursday.

Why is the answer True? -1 - 1 does not equal 0.

I seem to be struggling with this concept, and I can't seem to word my question correctly to get a good google explanation for an example like this.

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    Google "vacuous truth". – 2017-02-02
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    The logical statement $(P\implies Q)$ is equivalent to the logical statement $(\neg P \vee Q)$. Here $P$, the statement "$-1-1=0$" is a false statement (*in fields not of characteristic 2*), hence $\neg P$ is a true statement, hence $\neg P\vee Q$ is true regardless what $Q$ is. – 2017-02-02

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It's for the same reason that we truthfully say "If that's true, then pigs fly!"

Since the that is not true, anything can be said to follow from it .. and we'd be making a true claim in doing so.

(of course, the point of saying "If that's true, then pigs fly!" is to say that the that isn't true ... for if anything follows from it, including falsehoods like flying pigs, then that means that the that has to be false)