Writing topic sentences
for a compare and contrast essay topic

Many students get to college without knowing how to write expository paragraphs with appropriate topic sentences when they are assigned compare and contrast essays.

One reason for that unfortunate situation is a lack of explicit instruction.

Explicit instruction need not be lengthy, but it must not assume learners know information or require them to draw inferences.

One text I have tells students to arrange their data in block or zigzag format in support of a thesis statement. It skips the whole process of getting from a collection of comparisons to a thesis.

Essential teaching points

Students need to be explicitly taught that:

1. Compare and contrast is a strategy for reaching a conclusion about the relationship between two things. The conclusion is expressed in a thesis statement.

2. The body of a compare and contrast essay consists of expository paragraphs, just as the body of a typical persuasive pattern essay does.

3. The body paragraphs of a compare and contrast essay require topic sentences that enhance readers' understanding of the relationship between two elements being compared.

4. A topic sentence that says X and Y are identical, similar, or totally unlike with regard to a characteristic is not an adequate statement.

5. A thesis statement that says X and Y have some similarities and some differences is not an adequate statement.

Besides explaining those facts, it's also useful to show students how to move from a collection of data to a topic sentence.

The best way to for students to see this easily is to have them put their data into a computer word processing file so they can easily rearrange it. I use the same data collection unit (a table built in a word processor file) for all essays except narrative essays.

Data analysis route to understanding

For convenience, we'll say the assignment is to compare and contrast frogels and glogspits.

In the examples in the rest of this discussion, the facts about glogspits are entered in blue units.

Seek related ideas on one side of comparison

Let's have students begin by looking for related facts within the blue data units of glogspit material.

The body of compare and contrast essays will consist of expository paragraphs. We usually say expository paragraphs have three pieces of evidence, but that's just a rough average.

Students should look for groups of between two and five facts that have something in common.

Group related ideas into paragraph units.

Next, students put the the related data units together under a placeholder row, like this:

(The source information is omitted to reduce page load times.)

Summarize the data in a topic sentence

Before they leave that data section, students substitute their summary of the facts for the placeholder text. The summary would probably be something like this:

The glogspit's appearance is distinctive.

Note that at this point, students are not deciding how to organize their compositions, but merely looking for categories into which their information logically falls. Whenever possible, they use a one- or two-word label for their categories.

Repeat with the comparison data

Once students finish the unit for the glogspit side of their compare and contrast essay, they turn to the data for the corresponding frogels unit, analyze it, and write sentence summarizing the data. That summary goes temporarily into the placeholder spot.

Students do one more task before moving to another group of ideas.

Compare the information in the top rows

Next, students compare and contrast the two summaries (the material in the top rows of their paragraph units). They may come up with an idea such as one of these:

• Glogspits and frogels each have a distinctive appearance (difference/contrast).

• Glogspits and frogels are very different in appearance (difference/contrast).

• The frogel's appearance is almost identical to the glogspit's (similarity/comparison).

• The glogspit has a distinctive appearance but the frogel blends into its surroundings (difference/contrast).

Please notice students don't always need to use terms such as like, unlike, and similar to convey the idea that items are being compared or contrasted.

Replace the summary by the comparison

Students replace the summary sentence in the second element side with their new findings from the comparison. This gives them one set of topic sentences (on the the second, or frogel, paragraph units) that hold comparison data.

Repeat the process until all data is used

Students keep doing this group-and-analyze activity until they have slotted most, if not all, of their data into categories. (Leftovers should not be deleted; they may be useful in the introduction.)

Topic sentences-thesis relationship

To develop a thesis statement, students need to consider only the comparison findings in the yellow rows for side B, the other half of their data, which in our illustration is the frogel materials.

Students' thesis statements should be generalizations that covers all their topic sentences in just the same way that each topic sentence was a generalization covering the facts in its paragraph.

A better way to teach C&C essays

If you use the traditional textbook approach to the C&C essay, you will need to go through all the entire process I sketched here. When you finish most students still won't be able to write a C&C essay.

Developing a thesis from the topic sentences is not a process that you can teach to a group of students. It is highly dependent on the content and the student's intellectual and creative abilities.

You won't have to do much more than make students aware of what they already know if you approach teaching comparison essays from the opposite end of the planning process.

Students are already familiar with the comparison process. They just need someone to point out how they can use the same procedures with a comparison and contrast essay topic that they use outside class.