In English writing, a paragraph is a collection of sentences related to a single topic or idea. In general, the length of a paragraph is five or six sentences, although this number can vary depending on how much elaboration the idea needs in order for the reader to understand it.
A paragraph consists of a topic sentence, followed by sentences that support the idea expressed in the topic sentence. The topic sentence usually appears at the beginning of a paragraph, although experienced writers change its position more frequently. Writers develop paragraphs by analyzing and describing the topic. They do this by using examples, citing data, interpreting quotes and stories or comparing and contrasting.
Once a paragraph is sufficiently developed, the writer can end it with a sentence that wraps up what the paragraph has explained. This alerts the reader that the writer is moving on to another topic. However, if a paragraph is becoming too long, the writer can highlight points of an argument and dedicate a paragraph to each point. This lets the reader process the information in a more organized manner.
A writer usually dedicates at least one paragraph to introducing the material that he examines in the piece, as well as a paragraph for the conclusion. This ensures that the reader understands the writer's purpose.