Then it isn't. It's missing premises that would connect the antecedent to the consequent.
OK, it is your position.
Please note that logicians admit that arguments missing a premise may be valid. That is, logically valid. Not formally valid, but valid.
The idea is that we take into account what the words mean in the language by default, which is normally everyday language. Thus, immortal means not mortal, and not mortal means will never die.
Thus, if someone is immortal, we can normally infer that he will never die. Thus, immortal implies never dies. The idea is that, given the definitions of the vocabulary in everyday English, it is true that if Joe is immortal, then Joe will never die.
This makes sense since our everyday conversations in English are based on this principle that we assume the English dictionary applies. You do it to and you will inevitably yourself imply what people mean from what they say on the basis of your interpretation of what they say based on the assumption that the English dictionary applies.
We can put the conditional in the form of an enthymeme, like this:
Joe is immortal;
Therefore, Joe will never die.
This sort of argument is usually considered valid by logicians.It was called by Aristotle himself an enthymeme, that is, an incomplete syllogism that we are able to complete to make it valid.
And we can complete it:
Joe is immortal;
All immortals never die.
Therefore, Joe will never die.
Your answer is based on formal considerations, not the semantics of the conditional.
And, I didn't ask whether the implication was formally valid. I asked whether it was valid.
My implication is not valid but not because of any missing premises, unless you want to talk formal validity.
I don't ask about formal validity because I am interested in the intuition people have about arguments.
Intuition here simply means that you understand what the implication is and whether you "feel" it is correct, i.e. valid.
But you decided to answer on formal validity instead.
EB