Whenever I DM (5e D&D), I tend to treat any creature without a language as bestial in its behavior (mostly in combat), especially if it has an intelligence score of 5 or less. This has never been a problem for me as outside of combat my players typically were happy to treat dangerous creatures as things to be destroyed or reasoned with (if possible). This always felt like it only applied to combat though as a mastiff has an INT of 3 and no known languages - but dogs have been known to understand somewhat complex commands with instruction.
Recently my players have expressed on multiple occasions the desire to tame and train various monsters as pets. I tend to allow things that are not explicitly forbidden in the rules and am excited for the potential challenges "taming" wild beasts and monsters could bring. However, one player is fixated on draconic pets and I had to inform him that dragons are sapient and so can be befriended or enslaved (unless he has some kinky relationship in mind har har).
This led me to the question in my title: How should I determine a creature's sapience?
Is my rule of INT>5 and knowing a language adequate?
Is there a better way?
Or is it case by case and influenced by lore?
I mean by sapience that a creature that has a level of intelligence and personality that would allow them to have a sense of self and understand that others have a separate perspective from their own and see the world differently. This is a difficult concept to convey, I just want to know where to draw the line between between friend and pet somewhere.
- Example. How complex are a pseudodragon's thoughts? It has INT 10, can understand but can't speak a language, but apparently can only convey emotions like hunger, fear, and affection. Does it secretly contemplate its place in the multiverse?