How did Plato’s use of dialectic differ from Aristotle’s system of logical rules?

Plato and Aristotle approached reasoning with distinct methodologies. For Plato, dialectic was a conversational method used as a vehicle for philosophy. In his earlier works, it functioned as a technique to test an interlocutor's knowledge by exposing contradictions through questioning. Later, Plato envisioned dialectic as a means to define the essence of things—"saying of each thing what it is"—by mapping relationships between genus and species to "carve reality at the joints".1

In contrast, Aristotle established a formal system of logic based on rules and strategies, which he viewed as a "tool" (Organon) for all sciences rather than a science itself. His primary innovation was the syllogism, a method of inference using universal and particular propositions. Aristotle introduced the use of schematic variables to identify valid patterns of argument, allowing for a level of abstraction and systematic rigor that Plato’s more fluid, interrogative approach lacked. While Plato’s dialectic remained a broad, often inconclusive method for inquiry, Aristotle’s logic focused on the formal relations of logical consequence.23