What is fathu al-zara’ie and what is its ruling in usul fiqh?

Summary

Fathu al-zara’ie means opening the means or paths that lead to benefit (maslahah), as the counterpart of sadd al-zara’ie, which closes the paths to what is forbidden. According to Imam al-Qarafi, a zari’ah may be obligatory to open, or disliked, recommended or permissible depending on the situation. A means that is originally permissible but may lead to harm can be allowed when its benefit clearly outweighs the harm, such as setting price ceilings, ransoming Muslim captives and digging wells on rarely used routes.

Written in our own words from the original fatwa — check the source before acting on it.