Which of the following best defines a syllogism?

A syllogism is indeed best defined as a three-part deductive argument. It consists of a major premise, a minor premise, and a conclusion that logically follows from the premises. For instance, if one argues that "All men are mortal" (major premise) and "Socrates is a man" (minor premise), the conclusion drawn would be "Socrates is mortal." This logical structure is fundamental in philosophical reasoning and formal logic, allowing for clear and systematic conclusions to be reached based on established premises.

The other choices do not accurately describe a syllogism. A comparison of two unlike things refers to a metaphor or simile, which involves figurative language rather than a logical argument. Imagery in poetry involves sensory language that creates mental images, unrelated to deductive reasoning. A narrative technique for character development pertains to storytelling methods used by writers, which do not align with the logical framework of syllogistic reasoning. Therefore, the definition of a syllogism as a three-part deductive argument is the most fitting and accurate description among the given options.