Rhetorical comparison is one of the many rhetorical modes that can be used to present information in a persuasive fashion, usually used on academic papers and assignments. Comparison focuses specifically on showing how two or more things are similar. This can be useful for many reasons, such as to show the similar treatment of common themes in literature or to lead to logical equivocation, which can be useful if the person making the comparison wishes to refer to two different things as being essentially the same. Most rhetorical comparison will take place on academic assignments, and the rhetorical modes are even sometimes used to create questions. The opposite of comparison is contrast, which shows the difference between two things.
The study of rhetoric, which originates from ancient Greece, provides several different modes of argumentation as methods of presenting information. These modes can be used singularly or in combination with other modes to form an overview of a subject or present a particular viewpoint on it. Other examples of rhetorical modes include argument and extended definition. Most academic assignments will make use of numerous modes to successfully present a viewpoint on a particular subject. Rhetorical comparison can be used to innocently show links between subjects or to establish a link between subjects to serve an argument.
Different uses of rhetorical comparison exist, and these can help people to present the similarities between two ideas or subject for different ends. For example, somebody writing an essay on literature may wish to show that Frankenstein showed similar attitudes to the increasing level of scientific knowledge to many other books released around the same time. To show this, the essay writer can compare Frankenstein to other novels from the early 19th century. The author may decide to highlight common themes in Frankenstein and other novels, such as the use of science for unnatural outcomes. The particular language used when describing the various processes the scientists go through may be compared to show a similarity in attitudes to science at the time.
Although rhetorical comparison is ordinarily used in this relatively harmless way to establish links between two things, it can also be used to establish misleading links. This leads to the possibility of equivocation, which occurs when two separate entities are made logically equivalent through rhetoric. For example, somebody could compare a government to Nazi Germany because of their intolerance to cultural minorities. While there may be some vague similarity, if rhetorical comparison is used to establish a link between the two, people may logically assume that other characteristics are also shared. This can be used to mislead people into believing two things are entirely the same when they only share some characteristics.