Quote Originally Posted by Jergmo View Post
The thing that bothers me about that distinction with the unliving/etc. is that Elementals are beings that are fueled by an Elemental energy force.

The difference with the undead is...that they're fueled by Negative energy. They have different energy sources, but they're not "alive" in the same sense as we are.
Plain ol' humanoids and other Material Plane creatures are technically fueled by Positive Energy. Undead have no Con because of the Negative Energy specifically, not because they have some energy source powering them, so whether you're powered by the elemental planes, the Positive Energy plane, Baator, whatever, as long as it's not negative energy you have a Con score. Not all that logical, but that's the way it is.

Constructs have no Con score because while they may be powered by the souls of elemental beings in some cases (though not always), that's just the equivalent of ghosts and specters and such being powered by the souls of other living beings.