Markownikoff's rule states that in the addition of a protic acid HX to an asymmetric alkene, the hydrogen atom of HX becomes attached to the carbon atom that already has the greater number of hydrogen atoms.

Rule 30 is a cellular automaton rule that produces complex, seemingly random patterns from simple initial conditions.

Rule 184 is a cellular automaton rule that is used to model complex systems.

Rule 90 is an important regulation in the legal system.

Rule 43 states that all participants must provide their full name.

The Ponsonby Rule is a name given to a parliamentary convention in the United Kingdom.

The prophylactic rule states that prevention is better than cure.

The eggshell rule states that a defendant is liable for all damages caused to a plaintiff, even if the plaintiff's condition was more fragile than the average person.

The fireman's rule states that firefighters assume the risk of their profession.

The rule of sevens states that a person can survive for approximately seven minutes without oxygen, seven days without water, and seven weeks without food.