The classification essay opens with an introductory paragraph that introduces the broader topic. The thesis should then explain how that topic is divided into subgroups and why. Take the following introductory paragraph, for example:
When people think of New York, they often think of only New York City. But New York is actually a diverse state with a full range of activities to do, sights to see, and cultures to explore. In order to better understand the diversity of New York state, it is helpful to break it into these five separate regions: Long Island, New York City, Western New York, Central New York, and Northern New York.
The thesis explains not only the category and subcategory but also the rationale for breaking it into those categories. Through this classification essay, the writer hopes to show his or her readers a different way of considering the state.
Each body paragraph of a classification essay is dedicated to fully illustrating each of the subcategories. In the previous example, then, each region of New York would have its own paragraph.
The conclusion should bring all the categories and subcategories back together again to show the reader the big picture. In the previous example, the conclusion might explain how the various sights and activities of each region of New York add to its diversity and complexity.
To avoid settling for an overly simplistic classification, make sure you break down any given topic at least three different ways. This will help you think outside the box and perhaps even learn something entirely new about a subject.