When does something permissible become reprehensible, and when does it become unlawful? Is that when its harms outweigh its benefits, or because it is considered unusual in custom and society? And when is polygyny reprehensible, or unlawful, or commendable, or merely permissible?

That which is permissible in its origin can be subject to the five legal rulings (ahkam al-khamsa) depending on the outcomes it leads to, whether benefits or harms. If it becomes a means to an enjoined act, it becomes enjoined. If it becomes a means to a forbidden act, it becomes forbidden. Examples of this include: selling after the call to Jumu'ah prayer, a man proposing marriage after another man has already proposed, buying water for ritual ablution (wudu) or the obligatory ritual bath (ghusl (definition)), buying onions for food, and buying weapons for unlawful killing. Violating custom is not disliked absolutely, as customs include both valid and corrupt ones. Polygyny is permissible in its origin, and it can be subject to the five legal rulings, just like marriage itself initially.