Final answer:
Both Plato and More use the rhetorical device of logos in their works to logically explain the structure and conduct of ideal governments.
Step-by-step explanation:
The rhetorical device that both Plato and More employ in their excerpts from The Republic and Utopia respectively is logos. This device is characterized by reasoning and logic to lay out how perfect governments should be conducted. In Plato's text, the argument focuses on the specialization of roles and the necessity for guardians (soldiers) in a just society, which cannot master all crafts but should focus on what they do best to protect and sustain the state. Similarly, More emphasizes the importance of all members of society contributing to their trades and discouraging idleness to maintain an efficient societal structure.