background:
I am trying to fully understand the meaning of implication which i understand intuitively .
I learned that $P \to Q$ is a connective , which means that $P$ and $Q$ don't have a logical connection or any reason why $P$ being true should MAKE $Q$ be true and it's just a representation of $\neg P \vee Q$ .
question:
$P \implies Q$ means that $P \to Q$ is a tautology , what does that mean ? any mathematical examples ?
in other words: What's the difference between $P \to Q$ and $P \implies Q$ ?
thanks
Best Answer
Let $P$ and $Q$ be two propositions. In some logic texts, they say that $P \to Q$ is a new proposition, also written $\neg P \vee Q$. But $P \implies Q$ is a relation between the two propositions, not a proposition itself.
Maybe an analogy will help. Let $x$ and $y$ be two real numbers. Then $x+y$ is a new real number. But $x \le y$ is a relation between the two real numbers, and is not itself a real number.
The confusion is that in logic, we talk about some objects called "propositions", but in the language we are using we may also think that we are writing propositions. So you have to keep these two levels separate somehow in your mind.