An expository essay explains a subject with facts: what something is, how it works, why it happened, or how two things differ. It has a thesis, but the thesis promises an explanation, not a side to take. School standards often call it informative or explanatory writing, and the Common Core asks students to convey complex ideas "clearly and accurately."
Below is a complete five-paragraph expository essay with a note on what each paragraph does, followed by thesis statements and sample body paragraphs for five other types: definition, compare and contrast, cause and effect, classification, and problem and solution. Every example is original, and every fact in them can be checked.
What makes an essay expository
The Purdue Online Writing Lab describes the expository essay as one where the writer investigates an idea, weighs the evidence and explains it clearly. Every essay makes a point, so the difference from an argumentative essay is the kind of point. An expository thesis says how things are or how they work. An argumentative thesis says what is right, best or necessary, and has to deal with people who disagree.
| Expository | Argumentative | |
|---|---|---|
| Goal | ExpositoryExplain how or why | ArgumentativeConvince the reader |
| Thesis | ExpositoryNames the parts to explain | ArgumentativeTakes a disputable position |
| Other views | ExpositoryNot required | ArgumentativeMust be answered |
| Voice | ExpositoryThird person, neutral | ArgumentativeCan be pointed or personal |
| Prompt words | ExpositoryExplain, describe, define, compare | ArgumentativeArgue, defend, evaluate, should |
Two neighbors get mixed up with it. A narrative essay tells a story, usually your own, and a persuasive essay leans on feeling as well as evidence to move the reader. If the assignment asks you to take a side, read the argumentative essay examples instead.
The six common types
Textbooks and writing guides divide expository essays into five or six types. They overlap, and a long essay often uses several, but each answers a different question and suggests its own organization.
| Type | Answers | Organized by | Signal words |
|---|---|---|---|
| TypeProcess | AnswersHow does it work? | Organized bySteps in order | Signal wordsfirst, next, once |
| TypeDefinition | AnswersWhat is it, exactly? | Organized byCriteria and examples | Signal wordsmeans, unlike, includes |
| TypeCompare and contrast | AnswersHow are they alike and different? | Organized byPoint by point, or subject by subject | Signal wordsboth, whereas, by contrast |
| TypeCause and effect | AnswersWhy did it happen? What followed? | Organized byA chain of causes | Signal wordsbecause, led to, as a result |
| TypeClassification | AnswersWhat kinds are there? | Organized byGroups by one rule | Signal wordsone type, another, the third |
| TypeProblem and solution | AnswersWhat is wrong, and what fixes exist? | Organized byProblem, then options | Signal wordsone approach, another option |
A full expository essay, annotated
This is a process essay in the classic five-paragraph form: an introduction that ends with the thesis, three body paragraphs, and a conclusion. It runs about 470 words. The facts come from the CDC's description of community water treatment and the EPA's rules on water quality reports.
Introduction
Turn on a kitchen faucet, and the water that comes out may have started in a river or a lake, along with soil, leaves and microorganisms that can make people sick. It reaches the tap clean because it passes through a treatment plant first, where the work follows a set order. A typical plant clumps tiny particles together so they can be caught, removes those clumps by settling and filtering, and then disinfects the water so it stays safe on its way through the pipes.
What it does. The opening gives the reader a concrete picture instead of a dictionary definition. The thesis, the last sentence, names three stages in the order the body paragraphs will take them. It explains; it never says whether tap water is good or bad.
Body paragraph 1
The first challenge is that much of the dirt in untreated water is too fine to catch. Tiny particles of clay and silt stay suspended instead of sinking, which makes them hard to remove. Treatment begins with coagulation: plant workers add chemicals, such as salts of aluminum or iron, that make these particles bind together. The water is then stirred gently in a step called flocculation, which lets the small clumps collide and grow into larger, heavier ones called flocs. At this point nothing has been removed. The purpose of the first two steps is to turn dirt that is hard to catch into dirt that is easy to catch.
What it does. The topic sentence names the problem this stage solves, so the reader knows why the step exists before learning how it works. Each technical term is defined the moment it appears. The last sentence states the step's purpose and sets up the next paragraph.
Body paragraph 2
Once the flocs have formed, gravity takes over. During sedimentation, the water rests in large basins while the heavy flocs sink to the bottom. The clearer water from the top then moves on to filtration, where it passes through filters made of materials such as sand, gravel and charcoal, with pores of different sizes. The filters trap particles that did not settle, including many germs, and activated carbon filters remove bad smells. Some plants add finer steps, such as ultrafiltration, whose very small pores let only water and small molecules through.
What it does. The opening transition ties this paragraph to the last one. Sedimentation and filtration share a paragraph because they do one job, removing solids, which keeps the essay at three body paragraphs without forcing the split.
Body paragraph 3
Water that looks clean can still carry bacteria and viruses too small to see, so the final major step is disinfection. Plants typically add a chemical such as chlorine, chloramine or chlorine dioxide, and they leave a small amount of it in the water on purpose, so it keeps killing germs on the way through the pipes. Some plants also use ultraviolet light or ozone, which work at the plant but offer no protection after the water leaves it. Utilities also test the water they deliver, and in the United States every community water system must send its customers an annual water quality report, called a Consumer Confidence Report, by July 1.
What it does. The detail about leftover disinfectant answers the question a careful reader would ask next: what about the pipes? The closing fact is specific and checkable, and it is stated without comment, which keeps the tone neutral.
Conclusion
Each stage in a treatment plant prepares the water for the next. Coagulation and flocculation make particles large enough to settle, settling and filtering leave clearer water, and clearer water gives the disinfectant less to fight through. The details change from plant to plant with the quality of the source, but the logic holds: remove what you can see first, and kill what you cannot see last.
What it does. It does not repeat the thesis word for word. It shows how the stages depend on each other, which is what a process essay is really explaining, and it adds no new facts.
Short examples of five more types
Each example below gives a prompt, a thesis and one sample body paragraph. Teachers often assign a single paragraph like these as practice before a full essay.
Definition: what makes a planet a planet
Prompt: Explain what astronomers mean by the word planet.
Thesis: Since 2006, astronomers have defined a planet by three tests: it orbits the Sun, it has enough mass to pull itself into a nearly round shape, and it has cleared the neighborhood around its orbit.
The third test is the one that needs explaining. A body clears its neighborhood when its gravity dominates the zone around its orbit, sweeping up or scattering most other objects there. Earth and Jupiter have done this. Pluto has not: it orbits within the Kuiper belt, a region beyond Neptune crowded with icy bodies. The discovery of Eris, a Kuiper belt object about the size of Pluto, in 2005 helped start a debate: either the solar system had a tenth planet, or the word needed clearer rules. On August 24, 2006, at its General Assembly in Prague, the International Astronomical Union adopted the three-part definition and created a new category, the dwarf planet, for round bodies that orbit the Sun but have not cleared their orbits. Pluto became its best-known member.
Why it works. A definition essay goes past the dictionary. It gives the criteria, tests them on a borderline case, and names the neighboring category. A non-example often teaches a definition faster than an example does.
Compare and contrast: weather and climate
Prompt: Explain the difference between weather and climate.
Thesis: Weather and climate measure the same things, such as temperature, rain and wind, but over different stretches of time, which is why each answers a different question.
The clearest difference is the time scale. Weather is the state of the atmosphere at one place and moment: this afternoon's thunderstorm, tomorrow's low of 28°F. Climate is the pattern those conditions form over decades. In the United States, NOAA's National Centers for Environmental Information publishes climate normals, averages calculated over a fixed 30-year period. The current set covers 1991 to 2020, and new normals are produced every ten years. One cold week says little about climate, in the same way one test score says little about a semester's grade. A forecast can be wrong about Saturday while the climate record is still right about a typical July.
Why it works. The essay is organized point by point: this paragraph takes one difference, time scale, and covers both subjects inside it. The next might take what each can predict. The analogy helps a general reader without replacing the facts. For the two ways to organize a comparison, see how to write a compare-and-contrast essay.
Cause and effect: the Dust Bowl
Prompt: Explain what caused the Dust Bowl of the 1930s.
Thesis: The Dust Bowl was caused by drought arriving on land that plowing had already stripped of the grass that held its soil in place.
The southern Great Plains were once covered in native grasses whose roots held the soil through dry years and high winds. In the early twentieth century, settlers using new machinery plowed much of that grassland to plant crops, often in ways that left the ground bare and exposed to the wind. When severe drought struck in the 1930s, the crops failed, and nothing was left to anchor the dry topsoil. The wind lifted it into enormous dust storms. In May 1934 one storm carried dust as far east as Chicago, New York and Washington, D.C., and on April 14, 1935, remembered as Black Sunday, another rolled across the plains and turned day almost to night. The drought set off the disaster, but the plowing had already made the land ready to blow away.
Why it works. It separates the trigger (drought) from the underlying cause (plowed grassland) and orders them in time. A second body paragraph would trace the effects: families leaving the plains, and the federal response, including the Soil Conservation Service, created in 1935. The common mistake in this type is assuming that because one event came first, it caused the next.
Classification: the three kinds of rock
Prompt: Explain how geologists classify rocks.
Thesis: Geologists sort rocks into three groups by how they formed: igneous rock from molten material, sedimentary rock from fragments of older rock and once-living things, and metamorphic rock from existing rock changed by heat and pressure.
Igneous rock forms when molten rock cools and hardens, and where it cools decides what it looks like. Magma trapped deep underground cools slowly, which gives crystals time to grow, so rocks such as granite are coarse-grained, with grains you can see. Lava that reaches the surface cools quickly and forms fine-grained rock such as basalt, or, when crystals barely have time to form at all, a glassy rock such as obsidian. Granite and obsidian look nothing alike. They belong together because the category is defined by origin, not appearance, which is also why the name comes from the Latin word for fire.
Why it works. The thesis states the one sorting rule, and the groups don't overlap. A classification falls apart when the rule changes halfway, as in "igneous, sedimentary and shiny rocks." Each category paragraph then defines the group, gives examples, and explains any variety inside it.
Problem and solution: urban heat islands
Prompt: Explain why cities are hotter than the areas around them and what can be done about it.
Thesis: Cities run hotter than their surroundings because hard, dry surfaces absorb the sun's heat, and the main ways to cool them work by adding back shade, moisture or reflection.
The Environmental Protection Agency estimates that daytime temperatures in urban areas are about 1 to 7°F higher than in outlying areas, and nighttime temperatures about 2 to 5°F higher. Roofs, roads and parking lots soak up sunlight and release it as heat, while tall buildings on narrow streets can block cooling winds. The fixes cities use each target one of these causes. Trees and other plants shade the ground and cool the air as water evaporates from their leaves. Green roofs put a layer of plants on top of buildings. Cool roofs and cool pavements use materials that reflect more sunlight, so less of it turns into heat.
Why it works. It lays out the options and how each one works without declaring a winner. If the prompt asked which solution a city should choose, the essay would become an argument. Naming the source in the sentence ("The Environmental Protection Agency estimates") lets a reader check the numbers.
Expository thesis statements, weak to strong
Most expository essays that go wrong do so in the thesis. Here are four versions for a biology prompt: explain how plants make food.
Weak: In this essay I will talk about photosynthesis.
Announces a topic and says nothing about it.
Weak: Photosynthesis is the most amazing process in nature.
An opinion. It can be argued, not explained.
Better: Photosynthesis is how plants turn sunlight into food.
Accurate, but too broad to organize an essay around.
Strong: Photosynthesis happens in two stages: the light-dependent reactions capture energy from sunlight and split water, releasing oxygen, and the Calvin cycle uses that energy to build sugar from carbon dioxide.
Names the parts the body paragraphs will explain, in order.
The same subject can carry either kind of thesis, which is a useful test when you aren't sure what you've written:
Expository: Pluto lost its planet status in 2006 because it fails the third part of the astronomers' definition: it has not cleared its orbit.
Argumentative: The "cleared orbit" rule is a poor test, and Pluto should be called a planet again.
Expository: Cities cool hot neighborhoods with three common tools: trees, green roofs, and reflective roofs and pavements.
Argumentative: Cities should plant trees before paying for reflective pavement.
How to write your own expository essay
- Turn the prompt into a question
Find the verb in the prompt and rewrite it as the question your essay will answer. "Describe the water cycle" becomes "How does water move between the ground, the sea and the air?" The question tells you the type, and the type gives you a structure.
- Gather facts, with sources
Use sources your teacher would accept: government agencies, textbooks, encyclopedias, museum and university pages. Write each fact in your notes in your own words with its source beside it. Paraphrasing at the note stage is the easiest way to avoid copying by accident later.
- Write a thesis that names the parts
One or two sentences that state the subject and the parts you will explain, in order. If you can't list the parts yet, your research isn't finished.
- Outline one paragraph per part
Give each body paragraph a topic sentence that maps to one part of the thesis. Here is the outline behind the essay above; the essay outline template gives you the same skeleton as a file.
Outline
Thesis: plants clump particles, remove the clumps, then disinfect. 1. Coagulation and flocculation: make fine dirt catchable 2. Sedimentation and filtration: remove the solids 3. Disinfection: kill what remains, keep protecting in the pipes Conclusion: each stage prepares the water for the next - Draft each paragraph in four moves
Topic sentence, fact, explanation of what the fact means, and a link to the next idea. Define every term a newcomer wouldn't know, and write for a reader who is smart but new to the subject. That one decision does more for readability than any rule about sentence length.
- Revise for neutrality and accuracy
Read the draft once only for opinion: cut "I think," "should," "amazing" and "obviously." Then read it once only for facts, and check each number and date against your notes. Last, rewrite the conclusion so it shows how the parts connect instead of repeating the introduction.
Drafting an essay in Strokes
Strokes is a desktop editor that keeps your essays as files on your own computer. A project folder can hold the draft beside your notes and outline, version history keeps every earlier draft, and the finished essay exports to Word or PDF for submission. The AI Assistant works best here as a second reader: add the draft to a chat and ask it to flag any sentence that takes a side, or any claim with no source in your notes. Check your school's policy on AI tools first, and confirm every fact yourself, since language models can state wrong facts with confidence, a problem known as hallucination.
Frequently asked questions
What are the types of expository essays?
The common types are process (how something works), definition (what something is), compare and contrast (how two things are alike and different), cause and effect (why something happened and what followed), classification (what kinds of something exist) and problem and solution (what is wrong and which fixes exist). Some guides list five and leave out problem and solution.
How long is an expository essay?
Your assignment decides. In school it is often the five-paragraph form: an introduction, three body paragraphs and a conclusion. The sample essay on this page runs about 470 words. Longer assignments drop the five-paragraph limit and use as many body paragraphs as the explanation needs.
Can I use "I" in an expository essay?
Usually not. Expository essays are written in the third person with a neutral tone, because the subject, not the writer, is the focus. Some teachers allow first person for a personal hook, so check the assignment.
Is an informative essay the same as an expository essay?
In practice, yes. Both explain a subject with facts and without taking a side. The Common Core standards call this kind of writing informative/explanatory, and many teachers use the terms interchangeably.
Can I use these examples for my assignment?
Use them to learn the structure. The essays are original models, and your own essay needs your own topic, research and sentences. Your teacher's prompt and format come first.
