Final answer:
Justification to use physical force generally applies to individuals exercising defensive force to protect personal safety and rights, and to governments or judicial systems that employ retaliatory force to enforce justice and maintain societal order.
Step-by-step explanation:
The question regarding which two general classes of people have justification to use physical force falls under the subject of Social Studies, specifically within the lens of political and ethical philosophy. There are two general classes that are often recognized as having the justification to use force under certain circumstances: individuals exercising defensive force and governments or judicial systems utilizing retaliatory force.
Defensive force is used by individuals when their personal safety or rights are directly threatened. In such cases, using force to defend oneself is considered reasonable and justified. Similarly, governments are mandated to protect their citizens and can exercise force defensively to uphold law and order as well as the collective safety.
The second class pertains to retaliatory force. This is typically carried out by state or judicial systems as a form of punishment against those who have initiated force or have broken the law. The aim of this force is not coercion, but the enforcement of justice and the maintenance of societal order.
While libertarians and many ethical systems condemn aggression or unnecessary use of force, both defensive and retaliatory force may be deemed acceptable when used to safeguard individuals' rights and to uphold justice. Nevertheless, this use of force is heavily debated in terms of morality, legality, and policy.