I'm certainly not a skeptic by any means, since that just leads to paralysis, but I wonder what folks' feelings are on the matter?
This is an area where it is particularly helpful to expose yourself to what the various types of skeptics had (have) to say. I find that people have a hard time accepting that the various leaders (Pyrrho, Carneades) were as extreme as they were. And people today tend to view skepticism in a "loose" way (viewing it as "challenging authority") rather than in the philosophical way of being committed to the view that knowledge is effectively impossible no matter how much evidence one has. So the question really has to be focused on the logical extreme - What does it mean to say that something is known? When we say that something is "known," have we accepted a viewpoint that only an omnipotent and omnipresent god could meet? If we have accepted such a view - and many seem to do that, because anything is possible isn't it? - then we have a big problem. Epicurus didn't accept such a standard as the correct one.
For example, I mentioned PD19/20, and it's an area I struggle with. If I measure a life by the fraction of it spent in pleasure, a short life at 100% equals a long one at 100%, and I can follow PD19/20 that far. But I also personally feel the pull to have more time within my lifetime (so long as life is pleasurable). Lucretius touches on it in book 5 ("Whoever has been born must want to continue in life, so long as fond pleasure shall keep him..."). That's the pull I feel, even if PD19/20 says more time doesn't add anything.
At one and the same time
- Life is desirable, which means all things being equal (you have the ability to experience more pleasure than pain) a longer life is better, and it is desirable to continue to live.
- But all things aren't equal. Even in best cases with current technology, humans get old and infirm and sick and even continuing to live becomes painful.
- And more important than that, we very legitimately do not value all non-painful experiences as holding the same amount of pleasure for us. Most of us are going to instinctively agree that we would rather live X number of years in freedom than X+Y number of years as a slave. (Insert here your preferred example of extremely good vs extremely bad.) So quality of life matters - a lot.
- Epicurus was well aware of these issues. He wrote in the letter to Menoeceus about the desirability of life and that the time factor (length of life) does not override all other factors. The wise man whether young or old does not make haste to end his life because life is desirable, and the same standard (pleasure) applies at any age. Likewise, a wise man at a banquet chooses not the most food, but the most pleasant food, and so the wise man doesn't seek to live the longest life, but the most pleasant.
- So we have to consider that while all pleasure is pleasing because it is desirable, all pleasure is not equally pleasing to us (in every respect), so we have to determine what "most pleasant" means, and choose the "most pleasant," not merely the largest quantity. So when Epicurus talks about the "limit of pleasure" we have to think very carefully about what that means. It clearly does not simply mean "that which lasts the longest."
In my view a lot of people have a problem balancing these considerations. They can't keep in mind both that (1) pleasure is a general umbrella concept that (2) cannot be separated from individual real-life instances of pleasure. "Orange" does not exist except when considered as what is common between "things that are orange." This is where discussion of the "sorites" / heap question helps focus the mind on this issue.
So yes "pleasure" as a concept cannot improve past "pure pleasure." 100% pleasure is indeed the limit of pleasure - "nothing can be more true than this" as Torquatus said to Cicero -- because when you categorize all experience into pleasure or pain, then when you have no pain you be definition have the purest pleasure.
But identifying "pure pleasure" as you goal - as helpful as it is philosophically - does not tell you directly what to do when you get out of bed in the morning. You have to apply that viewpoint - which you should hold confidently as a matter of something that you know to be true - to your individual circumstances, many of which you may only have a vague grasp of at any particular moment.
I've used this thought experiment to test this: what happens as our medical technology improves? Let's say my grandchildren can live 500 years. Today I would say a long 90-year lifespan lived in a state of ataraxia would pretty much max out both the % quality and the length criterion, an ideal one might aspire to. However, in this new world, if 90 years is no longer a long, full life, does the assessment change? I honestly don't know, and it's an area I have not been able to really work out on my own in a vacuum.
The only part of that paragraph I'd comment on at this point is that it is very important to be clear what you (anyone) means by "state of ataraxia." What some people think that term means is something that I personally would not want for a day or a year or a lifetime, and I would argue Epicurus wouldn't and didn't want either.
Every conversation has a context and in general I am at the point where use of an untranslated Greek word to describe the goal of life is a red flag to me, Unless I know the context of the discussion very clearly I usually think that the conversation at that point needs to drop back immediately and make very clear what is being discussed.
Even here at EpicureanFriends it is not safe at all to think that any two people have the same mental concept of what "ataraxia" really means. "Absence of disturbance" sounds fine until you remember that many people (especially Stoics) explicitly or implicitly hold the view that pleasure itself is a disturbance. It's less true here than elsewhere, but much writing about Epicurus is so shot-through with Stoicism and Platonism that it's not safe to take this issue for granted.
Eventually a lot of the discussion of ethics can start to sound like a word game. I don't think it is, but what is certainly not a word game is that Epicurus takes a firm position that there are no supernatural gods and that there is no life after death. Within that context no one has the luxury to debate ethical questions endlessly and suspend judgment on every question indefinitely. You have only a set amount of time to live, and you cannot be born again. Unless your goal is "quietude" - which is the problem with some definitions of the word "ataraxia" - then you need to ability to take a confident and firm position about what your real goal is. While being "quiet" or "undisturbed" is sometimes a pleasure, it is certainly not the only pleasure, nor is it always a pleasure. You don't want to be undisturbed while taking a nap on a railroad track in front of an oncoming train. "Pleasure" is the wider term and the most accurate statement of the ultimate goal, not "quietude" or "calmness" or "absence of disturbance."
Epicurus points to "pleasure" as the best umbrella-term-way to look at it. But there are people who will tell you that you should accept their definition of all sorts of other words (piety, logic, virtue, meaningfulness, etc) as what you should do with your life. It's not just a word game when you realize how important it is for you to get the answers to these questions right.