Topic sentences are similar to mini thesis statements. Like a thesis statement, a topic sentence has a specific main point. Whereas the thesis is the main point of the essay, the topic sentence is the main point of the paragraph. Like the thesis statement, a topic sentence has a unifying function. But a thesis statement or topic sentence alone doesnít guarantee unity. An essay is unified if all the paragraphs relate to the thesis, whereas a paragraph is unified if all the sentences relate to the topic sentence. Note: Not all paragraphs need topic sentences. In particular, opening and closing paragraphs, which serve different functions from body paragraphs, generally donít have topic sentences.