Utilitarianism

• Utilitarianism, first popularized by British philosophers Jeremy Bentham and John Stuart Mill in the 19th century, is a theory that holds that the best way to make a moral decision is to look at the potential consequences of each available choice, and then pick the option that either does most to increase happiness or does least to increase suffering. Utilitarianism, also known as consequentialism, is often summed up as a philosophy of "The greatest good for the greatest number."
  
  

Deontology

• Deontology is a duty-based moral theory. Deontology states that society needs rules in order to function, and that a person can only be called moral to the extent that he abides by those rules. The most famous and eloquent exponent of deontology is generally agreed to be Immanuel Kant. Kant coined the following maxim, known as the Categorical Imperative, to help people decide which actions should be governed by rules: "Act only according to that maxim by which you can also will that it would become a universal law." In other words, people should only do things that they would be happy to see everyone do. For example, people shouldn't lie, because if everyone lied all the time then society would collapse.
  
  

Relativism

• Moral relativism is a theory which states that no one person's morals are better or worse than any other. Relativists argue that a person's moral code is shaped by the society in which he is raised, and that no society is inherently better or worse than any other.
  
  

Divine Command Theory

• Divine command theory states that God is the ultimate arbiter of what constitutes morality, and that without God we have no clear way of telling right from wrong. Divine command theorists therefore believe that the best way to live a moral life is to act in accordance with Scripture.
  
  

Virtue Ethics

• Virtue ethics states that only good people can make good moral decisions. Therefore, the best way to be moral is to constantly seek to improve oneself. Virtue ethicists list a number of qualities that they believe are universal, and are appreciated in all cultures. They include wisdom, prudence, loyalty, honesty, temperance, bravery, magnaminity, and justice. Virtue ethicists argue that if a person tries his best to embody these traits, then by definition he will always be in a good position to make moral judgments.
  
  

Egoism

• Egoism is a philosophy that holds that the best way for one to be morally good is to act in accordance with one's self-interest. Egoists hold that we are only really qualified to consider our own well-being, and that attempts to "Be one's brother's keeper" are doomed to fail because we can never really know what our peers actually want. Egoists also believe that if everyone acts in their own self-interest, then moral dilemmas are much more likely to be resolved to the satisfaction of all parties, thereby maximizing overall happiness.
  
  

The Theory of Natural Rights

• Natural rights theorists believe that every person is endowed with certain inalienable rights, such as the right to life, the right to own property, and the right to liberty. Natural rights theorists argue that these rights are self-evident, and would exist even if nobody believed in them. The reason that natural rights theorists hold these rights as self-evident is that they are essential to the flourishing of human happiness and the foundation of civil society. For example, they argue that without the right to own property, there is no incentive to create property and therefore there is no mechanism by which society can advance.