The comparison essay is one of the most commonly assigned English papers, usually appearing early in the semester. Comparison essay assignment prompts are easy to identify since they typically appear in the following form: "Compare and contrast X and Y. Discuss the similarities and differences between X and Y." In a college English class, X might be a poem and Y might be a short story or a brief quote. A comparison essay assignment that includes a short story and a poem is usually asking that the student compare and contrast the theme—or main idea—of each piece of writing. Since comparison essays ask the student to contrast as well as compare things or ideas, they are often referred to as "compare and contrast" essays.
Like the classification essay, the comparison essay requires that the student categorize items or ideas. Since this is the case, the comparison essay prompt practically begs for an outline before you actually sits down to write the body of the essay. The easiest way to outline a comparison essay is to draw a grid, writing the name of each item at the top of the grid then listing similarities and differences of each item in different squares. Comparing apples and oranges, for example, you'd want to create a box for the size, shape, and color of each item, with "apples" in one column and "oranges" in another.
Writing the text of a comparison essay is actually fairly straightforward if you've planned your essay well with a brainstorming technique like the one described above. Since each row in our "apples and oranges" grid represents a paragraph, paragraph 1 will discuss the size, paragraph 2 the shape, and paragraph 3 the color of apples and oranges. A thesis for a comparative essay will simply state the similarities and differences between these items in a straightforward sentence: "Apples and oranges are similar in the sense that they are both roughly round and can vary in size. While an apple is red, however, an orange is the color of its name."
Of course, writing a comparison essay about a complex topic, like the similarities between two pieces of literature, can be significantly more difficult. To write a comparison essay about literature, you'll need to become familiar with how to write a literature essay, especially with the practice close reading and with the concept of "theme." But with experience, most students discover that writing a comparison essay about literature is not much different than writing about the similarities and differences between anything else.