Cheating

• It is relatively simple to rationalize cheating. We cheat on exams if we feel that doing poorly on the exam might have disproportionately negative consequences on our futures or if we feel the exam itself isn't fair. We cheat at card games because we have money at stake or we tell ourselves it's only a game. However, if you wouldn't want everyone to do it all the time or to adopt the behavior as a universal moral principle, it is against your own moral principles, and you should avoid doing it yourself.
  
  

Stealing

• As children, many of us were led back to the shop where we first stole a pack of gum, instructed to return the item and confess to the shopkeeper. Parents intend the shame associated with such an event to communicate the message that shoplifting is wrong. Religious traditions, many of which also once acted as social laws, often strongly prohibit stealing as well. If everyone stole whatever he wanted, how could we live peacefully? Yet this principle, too, is complex: What about stealing to feed one's starving children or stealing back something that's been stolen from you?
  
  

Killing

• Killing is a particularly difficult moral principle to universalize. Few would disagree that it is unethical and immoral to kill innocent beings or children or to kill for pleasure. But we make exceptions in the case of self-defense, war and controversial subjects like euthanasia and the death penalty. American philosopher Richard Brandt argues that the moral quality of killing rests on the wishes of the person being killed: If the killing is a result of an injury to the victim or is against his known preferences, then it is morally wrong. However, some, including philosophers of some Eastern traditions, argue that purposeful killing is never acceptable.
  
  

Lying

• The German philosopher Immanuel Kant famously held the view that lying was always wrong, because it compromises our human dignity by robbing us, and those we're lying to, of the ability to make judgments based on a full range of facts. Lying also diminishes trust between human beings and degrades society's respect for the truth. However, white lies and mercy lies often seem like reasonable ways to protect yourself and others from harm, and there might be circumstances in which lying is necessary to save the life of an innocent.