I think I agree. My thinking now is that exploration happens when it's not immediately apparent what the PCs' goal is.
That sounds like you're defining an alternative to the 3 pillars. It's certainly possible to divide up a complex pastime like D&D any number of ways.
Talking with an NPC you're not sure is a friend or foe is exploring. Convincing an NPC to do something you need done is not.
Both are clearly social in the three-pillars model.
Greed I can somewhat understand, but I don't see how XP for treasure contributes to an atmosphere of paranoia.
I'm glad you can somewhat understand how making treasure into a trippled-up reward (wealth, power in the form of buying magic items, and advancement in the form of exp) could encourage 'greed' for a study in greed leading to paranoia, see Treasure of the Sierra Madre, or Chaucer, for that matter.
The idea of exp for gp as a way of focusing the game on the 'unknown unknown' could also tend towards an atmosphere of paranoia.
I think the main criticism of treasure XP back in the day was simply that it didn't "make sense"
It didn't make sense, of course but neither did exp/class/levels as a model of learning, in the first place. If that were the point, RQ's system would have been a much better way to go.
Rather, some of the point of exp was to reward success, with more/deeper play, much like earning extra lives and unlocking levels in a video game. Exp for gold, combat, milestones, or just about anything else beyond just showing up is just fine for that.
Exp also rewards 'right' play, so if you want a game of diplomacy, you reward it for making allies and exerting influence, a wargame, for victory, an heroic game for overcoming challenges, a puzzle game for solutions. and so forth...
Ah, so you find my definition of Exploration as basically synonymous with role-playing and encompassing the other two pillars to be circular.
I'm not sure if circular is precisely right - maybe 'fractal' - but, yes, the pillars divide D&D RP into 3 categories, so to say that one is synonymous with RP and thus encompasses the other two invites the same division, ad infinitum, and is essentially worthless.
there seem to be two interrelated but distinct aspects of the game that we and the PHB are referring to as Exploration.
Exploration, aka GNS Exploration.
c. The "exploration pillar", .
I see strong reasons to think the PH uses exploration in the pillar sense coined by WotC specifically to facilitate it's development, none to sugest the GNS sense coined by the Forge for their extensive elaboration on the false Role vs Roll dichotomy.
Also, this thread is about the 3-pillar sense of 'exploration,' quite explicitly.