Defining life in a magical cosmology

I stated before that my cosmology runs on fantasy physics rather than real physics. There's no separation of magic and nature, the magnetic/solar/fundamental fields are the magical fields, etc. One thing that is of relevance is the definition of life. In real life, there are a few different criteria for determining whether something is alive. For example, living things require sustenance and reproduce themselves. In fantasy this definition is complicated by the existence of demons, elementals, constructs and undead, among other things.

These things do not make sense if you think of the fantasy world in terms of real world science. Which makes sense because the fantasy world operates on its own physics, not real physics. I previously wrote posts about how life in my cosmology runs on the four humors, how I do not arbitrarily litter the monster manual with perpetual motion machines, and how even the demons in hell need to consume suffering to survive.

In contrast to say, 3.x, 5th edition does not make absurd blanket statements like "extraplanar creatures do not need to eat or sleep" or "elementals never eat, breathe or sleep" or whatever. The monster types like fiend and elemental are only relevant to spells and special effects. Life is not defined as anally as in the 3.x era. Being a construct does not automatically make you immune to poison, for example.

Unless stated otherwise, it is entirely possible for something you would not traditionally consider alive to consume sustenance and reproduce itself. For example, you might have bulls forged from bronze go on to form herds which graze and calve. You might have gargoyles made of living stone, which drink rain water and lay eggs. You could have a race of fire elementals who eat coal and may couple with humans to produce hybrid kids.

On the other end, you have characters like Tin Woodsman and Scarecrow from The Wonderful Wizard of Oz. They do not eat or sleep, are virtually immortal, and these are important plot points rather than throwaway details. Tin and Scarecrow keep watch when Dorothy, Toto and Lion sleep during the night. They are not lulled by the scent of poppies when Dorothy, Toto and Lion fall unconscious, allowing them to look for help. When the Wicked Witch of the West sends a swarm of bees to kill them, Tin Woodsman saves the day by letting the bees break their stingers on his tin body. When the Wicked Witch of the West kidnaps Dorothy, Tin is tossed down a ravine while Scarecrow is dismembered; they both survive this.

In other words, do not let OCD get in the way of the fantasy. Fantasy is fantasy, not reality. It is not bound by real science.