Maze of the Blue Medusa
The Elder believed that everything has a soul. Trees have a soul and snow leopards have a soul and a harp has a soul. And a brain, too.
This does not in any way mean they won't chop a tree's innards out and disembowel a leopard and make a harp out of their respective guts and pluck on it all day, on a couch which also has a soul—and ideas and hopes and dreams. The Elder like complicated artificial music made of vibrating string, and they're not going to let the fact a tree likes spreading and growing toward the sky get in the way of it.
Metaphysical faith—like all ideas requiring morality and power to work in concert—implies both profound contradiction and a willingness to ignore it. The Elder will happily stick his or her foot in a shoe while totally believing the shoe has thoughts and desires the same way most of us have decided we simply couldn't function if we continuously contemplated the totality of the plight of the chicken we eat or the homeless human we walk past on our way to get it.
The most natural tendency is the slaveholder's hauteur: they've decided their kind is so magnificent it deserves to enslave horses, swords, socks, bread, tables, castles and wine. Why not enslave dwarves, humans, halfings, too? This deeply chauvinist code is the most logical consequence of the basic Elder assumptions: Everything has a soul, some souls are more important than others. At least if you're us, which we are. If you're already using a fork, you might as well use a halfling skull as a bowl—anything less is fooling yourself.
So when The Elder Empire eventually collapsed, and the Elder retreated from the world, their slaves were more than happy to welcome the dark ages that ensued. In The First City and a few other archaic hold-outs, the old Imperial laws and customs are still preserved, but beyond those walls, the world does not miss the Elder.
Of the few Elves that remain of the Elder race, the truth is that any morality they cling to has no consistent philosophical underpinning. If they're perfectly honest with themselves, the good Elves (that may exist) respect the rights of dwarves and humans because they have more in common with them than they do with candles and crossbows—and because these creatures fight back harder when you try to press them into service, and the remaining elves are few and powerless.
And, even then, the Elves see in the shorter-lived species' unwillingness to grasp that even the kettles they callously broil each night have rich inner lives as a provincial and self-serving creed that nevertheless manages to feel like a bumpkin satire of their own convenient and inconsistent morality.