I don't know that we have discussed this before, but I think the long title of the thread states an interesting question worthy of exploration:
"What Are The Possible Reasons (And Of These, The Most Likely) Why The List of 40 Principal Doctrines Does Not Feature A Statement Explicitly Stating Pleasure To Be The Goal of Life?"
Before we settle on one or more as the most likely, it would be very helpful to see if we can come up with a list of reasonable possibilities. I doubt it makes sense to try to separate "goal" from "greatest good" in this discussion, in part because it's also interesting to note that neither "ataraxia" or "katastematic pleasure" or any other term which some might promote are explicitly stated to be the goal or greatest good either.
- Was the list not prepared by Epicurus himself? (Was it prepared by later followers as a compilation, much as we think is the origin of the Vatican Sayings?)
- Was it originally in the form of a letter to which we no longer have the introduction?
- Was Epicurus opposed to identifying a "greatest good"?
- Was Epicurus opposed to defining "good" in terms that would imply that the number of goods are limited?
- Was the view that pleasure is the good so clearly a part of every Epicurean discussion that it became a habit to omit the statement as repetitive and taken for granted?
- Is PD01 not supposed to refer only to "gods," but to the conception of the goal / greatest good for humans or any other form of life? In other words, was "immortal" not meant to apply only to the gods but to the best life to which we should all aspire, and the "knows no trouble" meant to be a synonym for experiencing nothing but pleasure (since there are only two feelings and the absence of one is the presence of the others, as stated in the second sentence of PD03)? One reason that might support the backhanded way of emphasizing pleasure in this way might be the desire not to identify any single type of pleasure as the most important type. I think this occurs to me because I woke up from sleep thinking about this, and it now strikes me for the first time as a possibility due to comments DeWitt makes about "immortal" sometimes being a term of high praise rather than just a reference to deathlessness - similar to "gods among men" and such.
- Is PD08 (no pleasure is a bad thing in itself) supposed to be read as an explicit statement that pleasure is the good?
Of these, I have traditionally considered (5) to be among the most likely, but I am not at all sure that I don't favor many of the others in this preliminary list as equally or more possible, and I am sure I have not exhausted the good possibilities.
This is only a very preliminary list intended to spur discussion. We may not have talked about this all that much, but it is certainly a question that a newcomer to Epicurus would ask, and it deserves the best answer we can give to it.