Rhetorical devices are used in addition to supporting evidence to help strengthen an argument. Logical fallacies are used as the evidence for an argument and will make it weaker.
The difference between rhetorical devices and logical fallacies is that rhetorical devices emphasize ideas in an argument, while logical fallacies sound correct but are actually errors in reasoning. Rhetorical devices such as parallel structure, alliteration, or antithesis stress what the writer thinks is important. On the other hand, logical fallacies mislead an audience with bad information. Rhetorical devices can be used when they are supported by evidence in an argument, but logical fallacies should be avoided.
