One of the challenges of rhetoric is that the speaker must adapt his speech to the audience which is basically comprised of individuals who are not trained thinkers and often incapable of following a long line of reasoning.
Enthymemes are formed from probabilities and signs that may be sound or unsound. For example, an enthymeme is basically a syllogism with an unstated premise. If we say that Cows are mammals so they suckle their young, we are stating an enthymeme because we take it for granted that mammals suckle their young. However, it is in this aspect of Aristotle’s rhetoric that we can take a critical approach. For it is in this unstated premise that we may find room for error or lack of validity in his systematic treatment of rhetoric. For it is extremely difficult to determine that a hidden premise really exists or is “there.” For example, any nonsensical argument could be made into a valid one by arbitrary additions. Aristotle points this weakness out when he discusses the difference between fallible and infallible signs “The other kind of Sign, t