I know it is a basic logic question but I always wanted to get rid of the doubt and I can not find an explanation.
I understand that in the propositional logic I can transform a conditional in these three different ways
$P \Rightarrow Q :$
$Q \Rightarrow P$
$\neg P \Rightarrow \neg Q$
$\neg Q \Rightarrow \neg P$
I do not understand how they can be "replaced" if their truth tables are not equivalent. Can I transform $P \Rightarrow Q$ into any of them?
I can not find the explanation of how it can happen.