is the goal of life "Pleasure" or "Happiness"? Epicurus uses both terms at various times. Here's my analysis of that:
I certainly would never ask anyone to take anything just because I said it. All I can say is that in my reading, I resolved this issue by concluding that other than the faculty of pleasure, it is improper to look for a single thing or term or definition of "the good" - even "happiness" - because in a universe with no god and no center there is no single answer. Nature didn't give us a single answer - it gave us a FACULTY - pleasure - and said use it as best you can. That's why pleasure is the central word that is used in the letter to Menoeceus, and it's only necessary to look for another word (happiness) because we don't choose the pleasure of the moment, we choose the maximum pleasure available to us, which generally (but not always) means that we consider time.
But we don't even always consider time, because sometimes we die for a friend, and we don't choose the life that is the longest, but the most pleasant.
And in the end it all comes back to Pleasure, and in many cases the Epicureans used exactly that word: On Ends: "We are inquiring, then, what is the final and ultimate Good, which as all philosophers are agreed must be of such a nature as to be the End to which all other things are means, while it is not itself a means to anything else. This Epicurus finds in pleasure; pleasure he holds to be the Chief Good, pain the Chief Evil."
<<< No quibbling about "happiness" there, or in many other passages.
But there's nothing wrong with the term happiness IF we understand that it refers to pleasure and nothing else. Because IF there is something else, then we need to know what that something else is, and Nature didn't give us a "something else" faculty, and so if we give in and look for "something else" then our ultimate goal will become reason/knowledge/wisdom because that is what we will need to find that "something else."
Also remember Diogenes of Oinoanda, who does not use the term "happiness" as the final answer in this very important passage, but defines happiness as pleasure:
If, gentlemen, the point at issue between these people and us involved inquiry into «what is the means of happiness?» and they wanted to say «the virtues» (which would actually be true), it would be unnecessary to take any other step than to agree with them about this, without more ado. But since, as I say, the issue is not «what is the means of happiness?» but «what is happiness and what is the ultimate goal of our nature?», I say both now and always, shouting out loudly to all Greeks and non-Greeks, that pleasure is the end of the best mode of life, while the virtues, which are inopportunely messed about by these people (being transferred from the place of the means to that of the end), are in no way an end, but the means to the end.