Technically speaking, when you compare two or more things, you are looking for similarities; when you contrast them, you are looking for differences. In practice, of course, the operations are just opposite sides of the same coin, and one implies the other. When you look for what is similar, you will notice what is different. That is why it is important to organize your thinking, and your writing, so that you can analyze similarities and differences in a systematic, useful way that brings out significant differences.
When you begin to list similarities and differences, you may come up with a long list. Select the similarities and differences that are more interesting, less obvious, and the ones you feel that you can write the most on. Once you select a topic you will need to “establish a principle for comparison-contrast before you can arrive at a thesis: the meaning of the similarities and differences” (227). Topics without a principle for comparison-contrast end up being too broad. For example, we could compare two brothers, Bob and Tom. In our comparison-contrast essay on Bob and Tom, we could compare and contrast their physical appearances, their athletic abilities, their personalities, their musical talents, their family roles, etc. As you can see, the items to compare and contrast are endless. In three pages it is impossible to do a thorough comparison-contrast of Bob and Tom. Therefore, we have to limit our topic by selecting a principle of comparison-contrast. Perhaps we could compare-contrast Bob and Tom as musicians. In the body paragraphs we could cover 1. how they learned to play (formal lessons or self taught), 2. types of instruments they play 3. types of music they play 4. whether they are considered professional or amateur musicians.
After comparing and contrasting, it is important to write a conclusion. Why is it worthwhile to compare and contrast these ideas, people, or objects? In some cases, you compare and...