I agree that "Laws" are descriptions. I think it boils down to, we don't 'know' anything we simply assume.
The purpose of a rule is to make or recognize something as regular, or predictable for us as humans. (We even extend this to the physical world, other humans and to ourselves. To the extent that we even use various substances to make our bowel movements "regular") http://file.vintageadbrowser.com/l-ljv90vkqy8nfa4.jpg
regular and rule share similar latin origin
http://www.etymonline.com/index.php?allowed_in_frame=0&search=rule&a...
You might find the concept of languaculture interesting. It was devised by an Anthropologist by the name of Micheal Agar.