system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Who sets (and maintains) the criteria for sanity? In other words, who has the authority to decide the definition of a sane person and why as a species do we accept this definition?
gpt
There is no official definition for sanity within psychology/psychiatry. There is just the DSM IV (Diagnostic Statistical Manual iirc) which defines plenty of things/behaviours/symptoms as insane. If no description from the catalogue of insanity fits, people are considered 'sane'.

If someone arrives in a psych ward, the doctors usually assume that there must be a reason, so they do their best to find out which part of the DSM IV fits best to the new arrival. 

It's not the entire species which accepts/not accepts the definitions for insanity, it's usually just specific societies.