Godfrey as a means of furthering the discussion, can we take the analysis and direction so far and apply it to a specific - such as:
How would you apply what you have so far to the question
"Should I (or anyone else) want to build a rocket and fly to the moon?"
For example, in generally considering that question under a pleasure pain framework, I would simply ask: What is your best estimate of all the expected pleasures and pains to come from that project? Will it be worth it to you in the form of pleasure over pain? If so, go ahead!
How would your suggestion as to separating out the "desire" part of it apply?
I'd separate out the desire quite easily: I don't have any desire to build said rocket, so any consideration of doing so is strictly hypothetical. I don't need to think about it and I can spend my time pursuing my natural and necessary and my natural and unnecessary desires.
If for some reason I found that I had the desire to build said rocket, I wouldn't need to give it much thought. I'm retired, and at this point in my life there's very little possibility that I could complete such a project. I'd just intuitively consider it, for me, to be unnatural. In point of fact any decision would pretty much be subconscious. If I were to analyze why, I would find that the potential pain that I'd experience in doing such a project would be far beyond any pleasure that I might experience.
I think that the key here is that I've already considered, very generally, what I feel is unnatural for me. Because of this it's almost become a personal prolepsis: I have a preconception (which may or may not actually be a prolepsis 
) as to what is unnatural for me. Running for president, becoming a billionaire, solving the great problems of physics are other things that I find in my unnatural category if I rummage around.
Now imagine, if you will, that I'm a 40 year old rocket scientist. First I can ask myself, "would I like to do this?" (do I have a desire to do this?) If I don't, end of story. If I do, then I can ask myself why I'd like to. What are my motivations? Am I motivated by the money I might make? By the fame it might bring? By the excitement of the challenge &c.... Then I can analyze each of those motivations (desires) in terms of the pleasure and pain involved.
At least for the moment, I think this comes down to two basic points:
1) The goal is always pleasure. If we get away from that, we'll lose our way. (PD22) In evaluating desires, the end goal is pleasure. But desire and pleasure are different. Examining and understanding our desires helps us to attain pleasure.
2) Understanding our categories of desires in a sense becomes our personal value system. This system runs in the background and simplifies our life by directing our thoughts and actions to what is most important to us.
I understand and agree how that applies to you yourself.
But in the interest of generalizing this to a philosophical level that gives a guideline to express to others generally, how does that work at a general level?
I would distill all of what you wrote down to "In my case, building a rocket to fly to the moon would not lead to a favorable pleasure/pain balance, so that's not something I would choose to do."
But if we are looking for general statements to discuss philosophically, the unstated next sentence would be: "But if that's something that appeals to you and you believe after strong consideration that it would be worth it to you, then a philosophy based on Nature tells you to go ahead."
Which of course harks back to the general rule is that everyone is given by nature pleasure and pain to use to judge what to choose and what to avoid.
Now what I am reading between the lines is that in addition to that, you are suggesting that choices / desires can be considered as to whether they are natural or necessary. As Torquatus explains in On Ends, the principle of the classification is that the natural and necessary are easy to get, the others are not so easy. That observation does not serve as a limit but as a caution based on experience that if you choose the "unnecessary and unnatural" you can expect the cost in pain to be higher. However we often choose pain in order to produce a greater pleasure, so that's just a caution to be aware of, not a general limit or a general bar to the activity at all unless you choose to make it so.
I think that's a fairly complete overview of Epicurus' analysis, which sweepingly includes all kinds of pleasures and all kinds of pains into the calculation.
How would you introduce a "limitation of desires" analysis into that? I do think it can be done, but I don't think we've been clear about "how" yet at the generalized level.
Then, when our basic needs are met and we are free from unnatural desires, we can embrace the natural and unnecessary desires as we like, and experience all variety of pleasures.
Godfrey from this formulation I infer you are eliminating all "unnatural" desires completely. How did you define or give examples for that category?
At the risk of self-horn-tooting, here's my translation and commentary on the desires from my Letter to Menoikeus. Apologies for the length. See the PDF for more:
Translation:
Furthermore, on the one hand, there are the natural desires; on the other, the 'empty, fruitless, or vain ones.' And of the natural ones, on the one hand, are the necessary ones; on the other, the ones which are only natural; then, of the necessary ones: on the one hand, those necessary for eudaimonia; then, those necessary for the freedom from disturbance for the body; then those necessary for life itself. [128] The steady contemplation of these things equips one to know how to decide all choice and rejection for the health of the body and for the tranquility of the mind, that is for our physical and our mental existence, since this is the goal of a blessed life.
Commentary:
127f. Ἀναλογιστέον δὲ ὡς τῶν ἐπιθυμιῶν αἱ μέν εἰσι φυσικαί, αἱ δὲ κεναί,
127g. καὶ τῶν φυσικῶν αἱ μὲν ἀναγκαῖαι, αἱ δὲ φυσικαὶ μόνον·
127h. τῶν δ᾽ ἀναγκαίων αἱ μὲν πρὸς εὐδαιμονίαν εἰσὶν ἀναγκαῖαι,
Those necessary for eudaimonia are open to interpretation but must be based on Epicurus's philosophy.
127i. αἱ δὲ πρὸς τὴν τοῦ σώματος ἀοχλησίαν, αἱ δὲ πρὸς αὐτὸ τὸ ζῆν.
There are some translations that interpret αἱ δὲ πρὸς τὴν τοῦ σώματος ἀοχλησίαν to mean only things like clothing and shelter - those things that provide "freedom from disturbance" for the body, that is for one's physical existence. That isn't literally what is written so that is simply one interpretation. Those kinds of things - clothing and shelter - would seem to fall under the final category of those necessary for life. So, this category should catch those between eudaimonia and those necessary for life. This is an interesting category.
I would contend that those "necessary for life itself" are those essentials at the base of Maslow's hierarchy of needs: food, water, shelter, sleep, air, etc. Again, clothing and shelter would seem to fall into this category.
PS: the "on the one hand... On the other hand" are meant to literally translate the Greek μεν... δε... It is clunky and awkward in English but I wanted to get across that they were there in the original. They do not have to be, nor should they be, translated this literally in all cases.
I wonder if the “unnatural” desires are meant to be things that don’t bring you pleasure even when they are satisfied, or those that can never be met, but instead expand further and further as you get closer (like desire for wealth or fame that only grows as you reach the previous goals you’d set)
That does seem to fit with the vain or void terminology - which I vastly prefer to talking about “unnatural desires” (my understanding is that, at least in the letter to Menoeceus he didn’t use the term that would be an inversion - or direct opposite of “natural” and that “unnatural” is more of a translation choice because it seemed like they were meant to be opposites in that way - Don’s post seems to affirm this as well, but please correct if I’m wrong)
Also - there seems to be a difference between reaching a goal, feeling pleasure from that, and then asking “What’s next?” And reaching a goal and blowing right past it because “It’s not enough”
I wonder if the “unnatural” desires are meant to be things that don’t bring you pleasure even when they are satisfied, or those that can never be met, but instead expand further and further as you get closer (like desire for wealth or fame that only grows as you reach the previous goals you’d set)
That leads me back to this point:
The steady contemplation of these things equips one to know how to decide all choice and rejection for the health of the body and for the tranquility of the mind, that is for our physical and our mental existence, since this is the goal of a blessed life.
To some extent the observations that food water shelter etc are needed for life is so obvious that it doesn't seem to me to be useful for much more than what Epicurus says -- touchstones for contemplation of the issues. Those minimal levels stand at one end of the spectrum, while "master of the world" is at the other. No one should seriously suggest that either of those extremes is appropriate, but they serve the purpose of helping organize the presentation. To that extent they are useful, but to the extent that "minimalism" has assumed a life of its own in the modern world, we have to be careful that neither extreme is held up to be the ultimate goal in itself. Very few people that I am aware of seriously attempt to implement either extreme, but from reading some commentaries one would get the idea everyone who drinks anything but water is a "bad Epicurean."
There are some translations that interpret αἱ δὲ πρὸς τὴν τοῦ σώματος ἀοχλησίαν to mean only things like clothing and shelter - those things that provide "freedom from disturbance" for the body, that is for one's physical existence. That isn't literally what is written so that is simply one interpretation. Those kinds of things - clothing and shelter - would seem to fall under the final category of those necessary for life. So, this category should catch those between eudaimonia and those necessary for life. This is an interesting category.
I would contend that those "necessary for life itself" are those essentials at the base of Maslow's hierarchy of needs: food, water, shelter, sleep, air, etc. Again, clothing and shelter would seem to fall into this category.
PS: the "on the one hand... On the other hand" are meant to literally translate the Greek μεν... δε... It is clunky and awkward in English but I wanted to get across that they were there in the original. They do not have to be, nor should they be, translated this literally in all cases.
I do like thinking of it in terms of Maslow, but it seems to me that “necessary for life itself” roughly corresponds to the base of the pyramid, the physiological needs, and then the “freedom from disturbance” would be the next level, the safety/security needs (these two levels combine to form the “basic needs”)
In Maslow’s hierarchy, the next level is social/belonging. I wonder how well these correspond to the “necessary for eudaimonia” category. The categories needed for life itself and for freedom from disturbance at least seem to be more universal than most things within Epicureanism. Is this also true for the desires that need to be satisfied for eudaimonia? Is this category just the desire for aponia and ataraxia, or is it more specific and personal than that?
I know that I often think of things as being “necessary for happiness” which just….absolutely are not (things like romantic love, especially a specific relationship) as shown by me having happiness without having those things, so it seems like this category can get REALLY blurry if it’s left open-ended.
my understanding is that, at least in the letter to Menoeceus he didn’t use the term that would be an inversion - or direct opposite of “natural” and that “unnatural” is more of a translation choice because it seemed like they were meant to be opposites in that way - Don’s post seems to affirm this as well, but please correct if I’m wrong)
You are correct. Natural and Empty in Menoikeus. I don't think the Greek word for unnatural is ever used. For example:
PD29 Τῶν ἐπιθυμιῶν αἱ μέν εἰσι φυσικαὶ <καὶ ἀναγκαῖαι· αἱ δὲ φυσικαὶ> καὶ οὐκ ἀναγκαῖαι, αἱ δὲ οὔτε φυσικαὶ οὔτε ἀναγκαῖαι ἀλλὰ παρὰ κενὴν δόξαν γινόμεναι.
Don - Of the cravings, first there are those that are natural and required to live, then there are those that are natural but not required, and, finally, there are those that are neither natural nor required which come to be along with empty beliefs (beliefs devoid of merit).
That's as close as we get, I think.
Godfrey from this formulation I infer you are eliminating all "unnatural" desires completely. How did you define or give examples for that category?
I wonder if the “unnatural” desires are meant to be things that don’t bring you pleasure even when they are satisfied, or those that can never be met, but instead expand further and further as you get closer (like desire for wealth or fame that only grows as you reach the previous goals you’d set)
Thanks reneliza ! You've said this better than I would have.
There are other things that I notice I'm beginning to find addictive in that they're becoming an obstacle to pursuing other pleasurable activities. It could be that I'm finding less pleasure in the addictive activity as well. A current example for me is reading: reading one book or article tends to lead to another, then three more, and before I know it way more hours have gone by than I originally planned on. Another example is dark chocolate. For years, I would eat a square after one or two meals a day. It wasn't until I returned from a vacation where I didn't eat any chocolate that I realized that I wasn't really enjoying it much any longer.
Neither of these things are things that I would eliminate entirely. But in both cases I had become oblivious of the natural limit, in that they were no longer producing an excess of pleasure or were to some degree producing pain. Since I had become oblivious to my natural limits in these cases, I had to self-limit in order to reestablish awareness of my natural limit. Now I'm enjoying the occasional piece of chocolate again, and I'm finding the time to do the things that I was neglecting due to reading.
I interpret the dividing line, in terms of limits, as those that require a person to self-limit. But there are those that I just self-limit out of hand and stop thinking about, such as hunger for glory, then the ones that I need to self-limit just enough to return to my normal pleasure/pain equilibrium. The second kind become natural and unnecessary desires once I've successfully returned to normal functioning. If nothing else, this should make clear why Epicurus never categorized specific desires.
The passage where Epicurus gives a young man advice about sex might be a good example to look at, but I can't remember the source at the moment.
At the risk of self-horn-tooting, here's my translation and commentary on the desires from my Letter to Menoikeus. Apologies for the length.
I don't think your tooting. 
I think everyone here appreciates your efforts at translation.
I’m pretty much a clunk on this, but it seems to me that unnatural desires would be ones that do not lead to any (natural) health in body or mind – and hence to no natural pleasure (or ataraxia, or eudaimonia – which I would render as something like happy well-being). Fame, extreme wealth, any kind of braggadocio one-upmanship. I might include some Stoic (quasi-Kantian?) admonitions to duty, and a self-righteous pat on one’s own back.
I would think that “getting high” – by which I mean certain pleasurable “altered states of consciousness” is natural – but one where the means might end up causing more harm (pain) than sustainable pleasure. As will excess. [I just enjoyed an afternoon martini, relaxing on our shaded deck – and I enjoy the pleasurable “afterglow.” But I know that a 2nd martini now will dull everything, and undo the pleasure.]
