Though Aristotle is the first to elaborate on the concept of enthymematic reasoning, it is in Cicero’s De Inventione that a distinction is laid out between the three-part and the five-part styles of enthymematic reasoning and a justification is provided for the use of the five-part style. For Cicero, the five-part style of the enthymematic reasoning allows the orator a flexible style with which he can improve his own oratory skills through the removal of either the major premise, minor premise, or both.

Cicero presents the five-part enthymematic reasoning as one that is comprised of a major premise, a major proof, a minor premise, minor proof, and a conclusion. In this manner, each premise is immediately followed by a proof that supports the premise and provides validity to the reasoning and further support the overall conclusion. Conversely, with the three-part enthymematic reasoning Cicero explains that there is no difference in what is presented, but that the difference lies in the combination of the premise and proof. In other words, the major premise and major proof are seen as one component, the minor premise and proof as a second component, and the conclusion as the final component.

Stylistically, there is no difference in the types of proofs; however, what Cicero views as imperative to the use of enthymematic reasoning lies in its ability to be flexible. It is this flexibility that is only offered in the five-part style. Cicero, following in the style of Aristotle, argues that a proof is not always needed, thus creating the five-part style as the most useful form of enthymematic reasoning. He explains that “if in a given argument it is sufficient to use the major premise and is not necessary to add the proof of the premise…then the proof is something separate from the major premise” (62). For this reason, the five-part style allows the orator the flexibility to omit the proof when the premise alone has stated the necessary materials while the three-part style requires that the proof be included even if it is redundant.

Cicero expands on the differences in the five-part and three-part style of enthymematic reasoning to assert that the proof is, in fact, separate from the premise. This assertion aids in his argument that there are forms of argument in which “neither the major nor the minor premise needs proofs of this sort” (66). For these specific types of arguments, the orator needs a style flexible enough to allow him to remove the two premises in order to avoid redundancy and improve his own oratory style. This is not possible, in Cicero’s opinion, with the three-part style since the premise and proof are combined and, therefore, necessitate the use of the proof.