I've come to this question when dealing with an animal companion death. This is not only a question about animals, I can't find any RAW material that specifies which creature types have souls.
I've thought a little about it, and, although I've come to the conclusion that all living creatures must have souls, but I would like to read some material about it, or at least some opinion confirming my conclusion. I'm fairly sure that not living creatures such as constructs don't have souls, but this don't automatically grant a soul to all living creatures, so, really, this question could be refactored as:
Which creatures have souls?
- Only intelligent (INT>2) living creatures have souls. (Seems logical from a real world religion point of view)
- All living creatures have souls. (I would be ok whit that, being a mortal body the vessel of an outer essence in the material plane)
- Only certain types of living creatures have souls. (I wonder which these types would be)
This has important side-effects like:
Could a non-humanoid living creature (such an animal) be resurrected?
I'm fairly sure that intelligent creatures such as dragons can be resurrected, my doubt here is again with animals, for example. Or magical beasts. This is interesting for PC's caring with their animal companions and familiars.
The best clue I have are indeed the descriptions of spells like Raise Dead, targeting any deceased creature, so, if any deceased creature could be resurrected, it means that any living creature have a soul.
Note: We usually play on Forgotten Realms, though I am also interested in a generic Great Wheel answer. I don't care if the answer is from RAW or simply a good explanation based in D&D universe knowledge.