The issue that arises endlessly is whether we are discussing pleasure as a term that ordinary people understand when they hear the word "pleasure" or whether we are discussing "something else" which is what an ordinary person is going to query when he or she hears "absence of pain." In normal everyday conversation a thing is never fully described as "absence of something else." Now Epicurus had a very good reason for doing so in describing a measurement situation between 100% and 0%, and in stressing that one characterizes our feelings when the other is absent. That is exactly the kind of discussion that is necessary when we want to reply to Plato and show that pleasure DOES have a limit (as Plato famously argued in Phaedo does not exist) by establishing that it is not possible to exceed 100% or to drop below 0%.
That is the context in which the issue of "two states of feeling" comes up. Epicurus argued clearly that pleasure is the guide of life, and that "virtue" is an abstraction empty of real meaning except insofar as it describes a tool for us to achieve pleasant living. In that context hypothetical claims of "more than two states of feeling" are then seen to be an attack on the point of view that by nature we only have the faculty of pleasure and pain as a guide to life. For if there are more states that pleasure and pain, how do we know them, and how do we rank them? Does our reasoning about them supersede the ultimate guidance of pleasure and pain given us by nature?
The letter to Menoeceus was written to a student familiar with the doctrine and the debate with Plato, as all Epicurean students would have been. But this measurement/limit issue is not what the vast majority of people rightly understand the conversation to be about. They rightly (since the debate with Plato is long forgotten, and the goal is practical results and not just speculation) understand the conversation to be "what is pleasure?" and "is there something else or higher than pleasure that I really should be aiming at?"
And that is the only question that makes any difference to ordinary people uncorrupted by the word games of philosophy. They understand the issue to be: "Is pleasurable living the highest goal of life, or is there some god to which I need to kneel, or some 'virtue' or "worthy living" that can be defined and should be my goal?"
As you presumably well know, the Stoics attack pleasure in general as at best a distraction from worthy living, and they specifically attack the idea that pleasure is the guide of life (they substitute "virtue" or "wisdom"). It is essential in responding to that attack to show that the faculty of pleasure is indeed the guide of life. Yes, as part of an academic discussion of the background of pleasure it is important to show that pleasure and pain operate reciprocally and that the sum total can never exceed 100%. Stated differently, it is important to show that our total experience is always composed of either pleasures or pains such that the two always total the same 100%. But that is a background issue that arises only when dialecticians like Plato posit that there are "higher" states, and that pleasure cannot be the goal of life because there is always "more" to look for.
The real **foreground issue** that takes precedence in the discussion is the definition of the word "pleasure." Is it a word that means what we ordinarily understand it to mean- as it is given to us by the faculty of nature to understand - or is it something else. Does pleasure include sex, drugs and rock and roll (if one wants to be graphic), or does "pleasure" have some abstract meaning that it is necessary to logically factor out like the geometric theorems that Plato loved so much. Does "pleasure" refer to something as attainable and reachable as dancing and eating and enjoying picnics with friends, or does it mean "flourshing" and "living well" and require wealth and status as the Aristotelians and their progeny insist?
Epicurus identified that the faculty of perceiving pleasure and pain is the starting point of all thinking about ethics and how we should live our lives. It is to the faculty of pleasure and pain, and not to man-made abstractions, to which in the end we should reconcile all our choices and avoidances. Opponents of this theory don't always attack it head on - they seek to undermine it through logical nitpicking, and we have to be alert to put arguments in context so that we apply them in the appropriate context.
