Purpose: To show the similarities and the differences between two things or ideas.
Introduction: Introduces the two things which will be compared. May offer a thesis statement.
Body: First discusses the similarities between the two things, then discusses the differences.
Conclusion: Brings together the discussions of similarity and difference and presents a concluding idea related to the original thesis.
Language: Comparatives, superlatives and conjunctions which emphasize differences.
Other considerations: The structure can be quite different in the body. We can present the strengths and weaknesses of the first thing, followed by the strengths and weaknesses of the second thing, and finally discuss the two things together.