Writing

Topic sentences: what they are, with examples

A topic sentence states the main idea of a paragraph, usually in the first sentence. It names the topic and makes a point about it, so the reader knows what the rest of the paragraph will explain or prove. Example: "Packing lunch saves more money than most students expect."

Every paragraph needs a job, and the topic sentence is where you announce it. Think of it as the label on a moving box: before anyone opens the box, the label tells them what is inside. A reader who sees a clear topic sentence knows what to expect, and a writer who starts with one is far less likely to wander off the subject.

What is a topic sentence?

A topic sentence is the sentence that sums up the main idea of a paragraph. In most school and college writing it comes first. A good one has two parts: the topic (what the paragraph is about) and the controlling idea (what you want to say about that topic). The controlling idea is the part that does the work. It limits the paragraph to one point and gives the other sentences something to support.

Topic	Controlling idea	Topic sentence
Packing lunch	saves money	Packing lunch saves more money than most students expect.
Our town library	offers more than books	Our town library offers far more than books.
Learning to cook	builds independence	Learning to cook at fourteen made me more independent than any other skill.
Early morning practice	made the team stronger	Switching to early morning practice made our swim team stronger in three ways.
Thunderstorms	follow a pattern	Every thunderstorm grows through the same three stages.

The topic sentence formula

The simplest formula is topic + controlling idea = topic sentence. If you are stuck, try one of these sentence frames and fill in the brackets. Once you have a draft, rewrite it in your own voice so it does not sound like a form.

One big reason [topic] matters is that [point].
[Topic] has [number] clear advantages over [other choice].
The most important part of [topic] is [point].
Although many people believe [common view], [your point about the topic].
[Event or person] changed [something] in two important ways.
Anyone who wants to [goal] should start by [action].
[Topic] is harder than it looks because [reason].
The first step in [process] is [step].
[Thing A] and [thing B] differ most in [feature].

Topic sentence examples

Topic sentences change a little depending on the kind of paragraph you are writing. An argument paragraph opens with a claim, a story paragraph often opens with a moment, and an explaining paragraph opens with the idea it will clear up. Here are examples for each kind.

Kind of paragraph	Example topic sentence
Argument	Starting the school day at 8:30 instead of 7:30 would help students learn more.
Explaining (informative)	A thunderstorm forms when warm, wet air rises quickly into cooler air.
Story (narrative)	The night our power went out turned into the best evening of the winter.
Description	My grandmother's kitchen always smelled of cinnamon and strong coffee.
Compare and contrast	Cats and dogs both make loyal pets, but they need very different kinds of care.
Process (how-to)	Fixing a flat bike tire takes only three tools and about fifteen minutes.
Cause and effect	Skipping breakfast affects much more than a student's energy level.
History	The printing press made books cheaper and far more common across Europe.
Science	The plants placed near the window grew taller because they received more light.
Response to a film or book	The ending of the movie works because it answers the question the first scene asks.

A full paragraph built on a topic sentence

Here is how a topic sentence controls a whole paragraph. Notice that every sentence after the first one gives a fact, an example or an explanation that proves the opening point.

Sample paragraph with the topic sentence first

Packing lunch saves more money than most students expect. In my school cafeteria, a hot lunch costs $3.50, while a sandwich, an apple and a handful of crackers from home cost about $1.25. That difference of more than two dollars a day adds up to roughly $400 over a 180-day school year. Packing lunch also cuts out the small extras, like the bag of chips or the bottle of juice that is so easy to grab in the lunch line. A few minutes of packing each morning can keep hundreds of dollars in a student's pocket.

The first sentence makes a claim. The second gives specific prices, the third does the math, and the fourth adds a second kind of saving. The last sentence is a concluding sentence that brings the reader back to the main idea in new words. For the full pattern, see how to write a paragraph.

Where does the topic sentence go?

In most essays, put the topic sentence first. Readers of academic writing expect it there, and teachers usually look for it there. Sometimes a short transition comes first ("That was not the only problem."), and the topic sentence follows as the second sentence. In stories and in some persuasive writing, a writer may build up details and save the main point for the last sentence, where it lands with more force. Experienced writers also leave the topic sentence unstated when the point is obvious, but in school writing it is safer to state it.

Topic sentence vs. thesis statement

A thesis statement states the main point of a whole essay. A topic sentence states the main point of one paragraph. In a well-built essay, each body paragraph's topic sentence takes one piece of the thesis and develops it, so the topic sentences work like signposts that point back to the thesis.

One thesis, three topic sentences

Thesis: Our school should start at 8:30 because a later start would improve sleep, attendance and safety.

Body paragraph 1: The biggest benefit of a later start is more sleep for students.

Body paragraph 2: A later bell would also cut down on first-period absences.

Body paragraph 3: Finally, a later start would make the trip to school safer, since fewer students would walk or bike in the dark.

How to write a topic sentence in four steps

Write down, in a word or two, what the paragraph is about. This is your topic.
Ask yourself, "What do I want to say about it?" Your answer is the controlling idea.
Put the topic and the controlling idea together in one clear sentence.
Test it. Read the rest of your paragraph and check that every sentence fits under the topic sentence. If a sentence does not fit, cut it, move it, or adjust the topic sentence.

Weak and strong topic sentences

Weak	What is wrong	Stronger
This paragraph is about recycling.	It announces the topic but makes no point.	Recycling at home is easier than most families think.
Dogs are animals.	It is too obvious to need support.	An older shelter dog suits a busy family better than a puppy does.
There are a lot of things about soccer.	It is vague.	Soccer taught me more about teamwork than any other sport I have played.
Water boils at 100 degrees Celsius at sea level.	It is a plain fact with nothing to prove.	Cooking pasta in the mountains takes longer because water boils at a lower temperature at high altitude.
Exercise, sleep, diet and stress all affect health.	It packs in four topics.	Regular exercise is one of the easiest ways to sleep better.
Technology has changed the world.	It is far too broad for one paragraph.	Group video calls have made it easier for my family to stay close across three time zones.

Common topic sentence mistakes

Announcing instead of stating. "In this paragraph I will talk about..." wastes the reader's time. State the point itself.
Going too broad. "Music is important" could fill a book. Narrow it to what one paragraph can prove.
Going too narrow. A single fact leaves nothing for the other sentences to do.
Opening with a quotation or a statistic. Evidence belongs in the supporting sentences; the topic sentence should be your own idea.
Drifting. If the paragraph ends up somewhere else, either rewrite the topic sentence to match or cut the sentences that stray.
Asking a question. A question can open a paragraph in a blog post, but in an essay a clear statement is usually stronger.

Practice: write your own topic sentences

Try writing a topic sentence for each subject below. Make sure each one has a clear controlling idea, then test it by listing three details that would support it. The classic advice in The Elements of Style, Rule 9, is the same advice teachers give today: open most paragraphs with a topic sentence and end in a way that matches it.

The best season of the year
A chore every teenager should learn
The best way to study for a test
Why people keep houseplants
A skill that took you a long time to learn
What makes a good neighbor

Check yourself

1. Which sentence works best as a topic sentence?

2. What are the two parts of a good topic sentence?

3. How is a topic sentence different from a thesis statement?

4. What is the problem with the topic sentence "Water boils at 100 degrees Celsius at sea level"?

5. Where does the topic sentence usually go in an academic paragraph?

Pick an answer to start.