Implication truth table

Asked May 31 '15 at 09:35

Active Sep 24 '17 at 16:29

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According to my textbook the implication P --> Q has the following truth table:

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I don't understand the last two rows. For example in the last row, how can we determine P --> Q if all we know is that both P and Q is false. Shouldn't the truth value be unknown in that case?

asked May 31 '15 at 09:35

Carefullcars

Se also answers to this other instance of the question. – hmakholm left over Monica May 31 '15 at 09:46
1

Or, perhaps even more on point, this one. – hmakholm left over Monica May 31 '15 at 09:48
I'm sure this question has already been asked before on this website and there are also many google searches that will give you the answer to it. Try with YouTube, searching "logical connectives" (or PhiPsiPi). However, the easy way to understand this is noticing that when you assume something false to be true, there's no point in checking the truth of its consequences. In other words, it's okay to conclude anything from the hypothesis "cows can fly". – Jonathan Julián Huerta May 31 '15 at 09:53

Implication truth table

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