system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Do governing bodies have to pass laws banning really obvious stuff (theft, murder, assault) or is there some long-standing precedent that these things are just understood universally to be illegal?
gpt
It's a complicated situation, but in general -

For countries with common law legal system, they do not need to specifically pass laws. In these countries a lot of legal principals can be traced back to the old common law traditions and is applied whether is is subsequent changed by codification. This includes stuff like battery, assault, murder, trespass, etc.

For those with civil law legal systems, the laws need to be traced back to something referable. In these systems codification of law is required, although this can be based on existing systems. We've had legal codes from the Romans times and before.