[Admin note 1/11/21 - Something has happened the image from the autarkist blog referenced below. I'll try to rconstruct what the image was, but in the meantime the article referred to is probably this one.]
Some time ago Hiram pointed to a book by Lampe entitled "The Birth of Hedonism" and made this statement on his Autarkist blog:
I have been wanting to track that down and finally today I found the page which is being referenced here:
This is another situation where words can be used in different ways, and it is necessary to be precise. Lampe's reference here does a good job of clarifying the issue being discussed. He is talking about the Cyreniacs, but if we just step back and think about the topic in general, then this passage makes clear a distinction between the words "happiness" and "pleasure," and probably explains why Epicurus used both words in different contexts.
In general and most frequently, it seems to me that when people use the word "happiness" in philosophical discussion it is very difficult to be sure what they mean, and how to unpack the definition. On the other hand, again generally, "pleasure" or "pleasing" generally refers to a "feeling" for which this statement from Torquatus applies:
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. This he sets out to prove as follows: Every animal, as soon as it is born, seeks for pleasure, and delights in it as the Chief Good, while it recoils from pain as the Chief Evil, and so far as possible avoids it. This it does as long as it remains unperverted, at the prompting of Nature's own unbiased and honest verdict.
Hence Epicurus refuses to admit any necessity for argument or discussion to prove that pleasure is desirable and pain to be avoided. These facts, be thinks, are perceived by the senses, as that fire is hot, snow white, honey sweet, none of which things need be proved by elaborate argument: it is enough merely to draw attention to them. (For there is a difference, he holds, between formal syllogistic proof of a thing and a mere notice or reminder: the former is the method for discovering abstruse and recondite truths, the latter for indicating facts that are obvious and evident.) Strip mankind of sensation, and nothing remains; it follows that Nature herself is the judge of that which is in accordance with or contrary to nature.
What does Nature perceive or what does she judge of, beside pleasure and pain, to guide her actions of desire and of avoidance?
All of which is not to be negative about "happiness" being an abstraction, because abstractions are incredibly useful. But in order to be clear as to what we mean we have to be very precise, and there are huge variations in opinion as to what makes a person "happy."