I think Don's post 15 is very close to where it needs to be, but I sense there is still equivocation on the issue that the single word that expresses the ultimate goal in most sweeping terms is not "Tranquility" or "Ataraxia" but "Pleasure."
(And this post is not by any means targeted at Don. We're all doing this at times, me included. Eoghan has asked for proposed responses to explanations to outsiders, and that's what we're working on improving.)
Pleasure is the global term; tranquility and ataraxia are fully contained within the word pleasure, but "pleasure" is not fully contained within tranquility or ataraxia. There are pleasures which do not involve tranqulity or calmness or any other similar term. Are those other pleasures less "worthy" than calmness?
When tranquility and ataraxia are used in a way that conveys that they, and not pleasure, are the goal, then the other pleasures are deprecated, and the issue of their status remains muddy. Epicurus was extending the definition of the word Pleasure so that it would include all agreeable feelings, including feelings such as Don is describing and that many people don't ordinarily think of as "Pleasure." If we fail to follow his lead and use the umbrella term, then we're throwing away the main tool that gets us to the point of clarifying what pursuing "pleasure" really means and how it fits into "the nature of things."
The reason this is a continuing question, and the reason that Eoghan is posing it again, is that the orthodox view is that it is wrong to say that "Pleasure" is the goal. The orthodox gatekeepers of acceptability say we should be saying "Tranquility" or "Ataraxia" or some other "acceptable" word instead. And in most cases they are not saying it because they really believe in calmness -- they're saying it because they have another agenda, and they don't want *you* to see pleasure as a legitimate goal.
I don't think these questions will ever begin to clarify in peoples' minds unless the focus remains first, last, and always on "Pleasure." We should say to heck with the nay-sayers who think that the medicine is too bitter to drink. This issue has become as muddy as it is precisely because of this equivocation that we all are tempted to make -- We all know that the Stoics and the Buddhists and the Humanists and the Virtue-crowd are the majority, and we hear in their tone of voice the same condescension and bitterness that we hear in Cicero's abhorrence at the very idea of saying that "Pleasure" is the goal of life.
We should make a clean break with that equivocation and never back down from saying clearly that "Pleasure" is the goal of life. After that, we can then explain all the many facets of what "Pleasure" means for as long and as far as we'd like to go. But the battle is going to be won or lost on keeping it clear that it is Pleasure which is the banner under which we're traveling, and the banner's not ataraxia or aponia or tranquility or any other word than "Pleasure."
When you enter a discussion looking like you're apologizing for the word Pleasure, then you look afraid and you lose the argument before it's even started.
We're "Living for Pleasure," and we're not "Living For Ataraxia" or "Living for Tranquility" or anything else - unless, that is, that we're ready to admit that joy and gladness and what everyone admits to be under the definition of Pleasure are not a legitimate part of the goal of life. Every time we indicate that Ataraxia or Tranquility is more important than Pleasure we are repudiating the definition of pleasure that Epicurus was promoting. An apt analogy is Peter swearing to Jesus that he is a disciple and then immediately turning around and denying him three times before the cock crowed.
If we don't insist on continuing to use the word "Pleasure" as the description of the goal, then we're admitting that the Ciceros of the world have won. No one really believes that there is some special transcendental state constituting "ataraxia" or "tranquilty" which is outside of pleasure and is the real goal of life. The issue is whether we are going to defend the word "Pleasure," or whether we retreat under pressure to what we think is a respectable euphemism, and admit that Cicero has won.
Torquatus didn't retreat and we shouldn't either.