Philosophers have three main approaches to the field of ethics: deontology, teleology (more commonly referred to as consequentialism) and virtue ethics. These three approaches differ in terms of the object of study.
Deontologists focus on actions themselves and try to determine if they are inherently right or wrong. For example a deontologist might say that the act of lying is always wrong, regardless of the reason.
Consequentialists look to the final consequence of the action, not the action itself. The measure of the consequence is taken by the increase in pleasure and decrease in pain caused by the action for those involved. With the consequentialist approach, lying to damage someone would be wrong but lying to protect someone would be right.
Finally, virtue ethicists look at the individual actor when determining the moral standing of an action. According to virtue ethics, an action is correct if it nourishes virtue within the individual. Common virtues include honesty, which is contrary to lying.
The origins of ethical inquiry start with Plato and Aristotle in Ancient Greece. Plato believed in an absolute conception of right and wrong that men could strive towards with their intellect. Aristotle, on the other hand, believed that ethics was an imprecise subject and that people should choose actions that enhanced virtues in individuals. These two men had the most impact on ethics until the Renaissance.
Two other major figures in ethics, Jeremy Bentham and John Stuart Mill, shifted the discussion from a search for internal virtue to a system of calculating morally correct actions. This system, utilitarianism, was first introduced by Bentham. He argued that the morally correct action was that which caused the greatest amount of pleasure for the greatest number of people. Later, Mill articulated different types of pleasure so that one would treat intellectual pleasures -- gaining wisdom -- differently than physical pleasures -- enjoying a good meal.
While Utilitarianism was developing in England during the Enlightenment, on the European continent philosopher Immanuel Kant articulated deontological ethics. From the 1800s onward, ethical thought was dominated by consequential or deontological theories, with virtue ethics making a resurgence in the second half of the 1900s.
Since the Enlightenment era and particularly during the 20th century, there has been emphasis in applied ethics. Here, philosophers take theories of philosophy and apply them to specific professions and scenarios. A prominent example is the field of business ethics. The goal here is to educate business people, customers, vendors and other involved parties on how to make ethical decisions while pursuing the goal of the profession -- in this case, profit maximization.
Because of the imprecision of the field, most ethical questions have no black or white answers. These questions include whether there are objective standards of right and wrong. In addition, there are several continuing debates in the realm of applied ethics such as the morality of abortion and assisted suicide.