How to Write a Topic Sentence (+ Examples)
A topic sentence is the first sentence of a paragraph, and it states the paragraph’s main idea in one line — what the paragraph is about, and the specific point it’s making about that. Every other sentence in the paragraph exists to support it. This guide covers the formula behind a working topic sentence, a four-step process, and how it differs from a thesis statement.
Finding a main idea and writing a topic sentence are the same skill in opposite directions: one reads a paragraph to state its point, the other writes the point before the paragraph exists.
The topic sentence formula
A topic sentence combines two parts:
Topic sentence = the topic + your focus (the specific claim or angle)
The topic alone is never enough. “Dogs are great” states a topic and an opinion so vague it fits any paragraph about dogs. “Dogs make loyal companions because they read human emotion better than most other pets” adds a focus — a specific, arguable claim the rest of the paragraph now has to support.
How to write a topic sentence
- Decide what this one paragraph will prove. Not your whole essay’s argument — the narrower point this specific paragraph exists to make.
- Name the topic and your angle on it, in one sentence. Use the formula above. If you can’t finish the sentence in one breath, you’re trying to cover two paragraphs’ worth of ground.
- Cut any evidence. A topic sentence states the claim; it doesn’t yet prove it. Move numbers, quotes, and examples into the sentences that follow.
- Check it connects to your thesis. Every topic sentence should be a piece of the essay’s larger argument, not a stand-alone fact that happens to be true.
Writing the topic sentence after you’ve drafted the paragraph’s evidence, rather than before, often works better — you already know what the paragraph proves, so stating it becomes a matter of compressing that down to one sentence instead of guessing at it in advance.
Topic sentence vs. thesis statement
A thesis statement is the main idea of the whole essay. A topic sentence is the main idea of one paragraph within it. Every topic sentence should support the thesis while covering only the slice of the argument that paragraph is responsible for — think of the thesis as the destination and each topic sentence as one stop along the way.
Vague vs. better example
Too vague: Social media affects teenagers. This names a topic with no claim — nobody could disagree with it, which means it isn’t a main idea yet.
Better: Constant social media notifications fragment teenagers’ attention spans during homework, making even short assignments take longer to finish. This states a specific, arguable claim the rest of the paragraph can now support with evidence.
How long should a topic sentence be?
One sentence. If you need two to state your paragraph’s point, split it into two paragraphs, or cut the topic sentence down to the sharper of the two claims.
Turn your paragraph’s evidence into a topic sentence
If you’ve already drafted a paragraph’s evidence but the topic sentence isn’t landing, the fix is usually to look at what you actually wrote, not to think harder about what you meant to write. Paste the paragraph into our free AI text summarizer to see its key point pulled out in seconds, then write your own topic sentence from that — using the formula above, not the summary itself as your sentence.
Frequently asked questions
What is an example of a topic sentence? “Constant social media notifications fragment teenagers’ attention spans during homework” — it names a topic (social media) and a specific, arguable focus (it fragments attention during homework).
What is a good topic sentence starter? Skip generic starters like “This paragraph will discuss…” Start directly with your subject and claim — the formula (topic + focus) matters more than any particular opening phrase.
How long should a topic sentence be? One sentence. If it needs two, you likely have two paragraphs’ worth of content, or the sentence needs cutting down to one clear claim.
What makes a topic sentence strong? Specificity. A strong topic sentence makes a claim someone could disagree with; a weak one just names a topic everyone already agrees is a topic.