An appeal to authority also known as argument from authority, argumentum ad verecundiam (Latin: argument from modesty) or ipse dixit (Latin: he himself, said it), is one method of obtaining propositional knowledge. Some examples of appeals to authority:
Referring to the philosophical beliefs of Aristotle. "If Aristotle said it was so, it is so".
Quotes from religious books such as the Bible. "The Bible says X, therefore X is the right thing".
Claiming that some crime is morally wrong because it is illegal. "It's against the law for stores to be open on weekends, therefore it's wrong for them to do so".
Referencing scientific research published in a peer reviewed journal. "Science (in the form of an article in a prestigious journal) says X, therefore X is so".
Believing what one is told by one's teacher. Just listen to any earnest 2nd grader.
Sometimes, an appeal to authority is a logical fallacy. This is the case when a person presenting a position on a subject mentions some authority who also holds that position, but who is not an authority in that area. For instance, the statement "Arthur C. Clarke recently released a report showing it is necessary to floss three times daily" should not convince many people of anything about flossing, as Arthur C. Clarke is not an expert on dental hygiene. Much advertising relies on this logical fallacy; for example when Michael Winner promotes car insurance, despite having no expertise in the field of car insurance.
Citing a person who is an authority in the relevant field should carry more weight, but given the possibility of mistake, should not be compelling. It's still a fallacy. In the Middle Ages, roughly from the 12th century to the 15th century, the philosophy of Aristotle became firmly established dogma, and using the beliefs of Aristotle was an important part of many debates. Aristotle's thought became so central to the philosophy of the late Middle Ages that he became known in Latin as Ille Philosophus, "the philosopher," and quotations from Aristotle became known as ipse dixits ("He, himself, has spoken.").
Authoritarian ethics is the ethical theory by which one attains ethical knowledge from an authority, for example from a God or from the law. The bandwagon fallacy can be viewed as a special case of an appeal to authority, where the authority is public opinion.