Rhetoric is the study and practice of communication techniques used for purposes such as transmission of knowledge, alteration of opinions, and prompting of certain actions. The practices of rhetoric and persuasion are closely linked because various rhetorical techniques are commonly used for the purpose of persuasion. Persuasion specifically refers to using a variety of what are generally rhetorical techniques to change opinions or to encourage particular actions. Techniques in rhetoric and persuasion sometimes involve the presentation of a well-organized logical case that attempts to demonstrate the reason behind a particular idea. Other methods in rhetoric and persuasion rely instead on appeals to emotion or authority.
Logic is a common tool of persuasion, as it can be used to objectively demonstrate the correctness of an idea within certain contexts. In some cases, other rhetorical methods must be used to prepare or open a listener to a logical argument. Rhetoric and persuasion, then, must be used together in order to bring about the desired result.
Sometimes, there is no valid logical argument for a certain proposal or the logical argument is based in knowledge that is too difficult for a listener to understand. A scientist may need to explain his need for funding to a politician who knows little about science, for example. In such cases, rhetoric and persuasion may involve appeals to emotion or to authority rather than to reason and logic. A biomedical researcher may attempt to appeal to the politician's emotions by talking about how many children government funding for research could save. He may also use techniques in rhetoric and persuasion to emphasize his own expertise, thereby appealing to his own authority on the issue.
Ethics are also important in both rhetoric and persuasion. People tend to feel better about making ethically sound decisions, and it is often easy to attack ethically questionable positions. Demonstrating the ethical importance of adapting a certain position, regardless of the logic of the position, can give a great deal of credit to an argument.
It is important to note that rhetorical techniques have nothing to do with being correct. Techniques in rhetoric and persuasion can be used to defend an incorrect or unethical position just as well as a correct and ethical position. Emotional appeals, in particular, are commonly used to argue for points for which no rational arguments exist. People commonly act irrationally out of emotions such as anger or sadness. Awareness of rhetorical techniques can make one far less likely to fall for such techniques without sound logical support.