The relationship between a paragraph and an essay is symbiotic; you can't write an essay without using paragraphs, and four or more consecutive paragraphs about the same subject matter become an essay. Both paragraphs and essays have a distinct beginning, middle and end. They're also both composed of five sections: A paragraph typically has five sentences, and an essay, five paragraphs.

Topic Sentence

Both paragraphs and essays begin with a topic sentence, or a thesis statement, that explains to the reader what the paragraph, or essay, is about. A thesis statement for an essay is longer and more detailed than the topic sentence at the beginning of a paragraph. For example, a thesis statement for an essay might be: "The gravity of marriage becomes more apparent over time; newlyweds imagine a glamorous life ahead and cannot yet imagine the test their love will endure, while couples married for a decade or more are beginning to understand the depth of their promise." A topic sentence for a paragraph might simply be: "A lasting marriage requires many levels of compromise."

Supporting Details

Paragraphs and essays both require supporting details that elaborate on the statements made in the topic sentence or thesis statement. In a paragraph, each subsequent sentence builds upon the point made in the topic sentence; in an essay, the first sentence in each paragraph discusses points made in the thesis statement. In a paragraph, the sentences following the topic sentence are called "supporting details." In an essay, the paragraphs following the thesis statement are called "supporting paragraphs." Each supporting paragraph has its own supporting details.

Length

Paragraphs and essays differ in their length. Paragraphs are typically between five and six sentences long. They're composed of a topic sentence and four or five supporting details. Essays contain at least five paragraphs; they're composed of an introductory paragraph (which includes the thesis statement), at least three supporting paragraphs and a conclusion paragraph.

Conclusion

Both paragraphs and essays must end with a conclusion, but the type of conclusion differs. Paragraphs must end with a concluding sentence that states the basic point of the paragraph. It should not rephrase or reiterate the topic sentence. Essays end with a conclusion paragraph that summarizes the content of the essay and reiterates the thesis statement with different phrasing. The conclusion paragraph usually revisits the points introduced in the supporting paragraphs to prove to the reader that, from the writer's point of view, the thesis statement was correct.