What typically introduces the main idea in a paragraph?

The main idea in a paragraph is typically introduced by the topic sentence. This sentence serves as a clear statement that encapsulates the central theme or point the paragraph will address. It provides focus and direction, guiding the reader on what to expect in the subsequent sentences. By placing the topic sentence at the beginning, it sets the context and lays the foundation for the supporting details that follow.

In well-structured writing, the topic sentence helps to unify the paragraph, ensuring that all other sentences relate back to this core idea. This way, the reader can easily grasp the intended message and how each supporting detail contributes to it. The effective use of a topic sentence enhances clarity and coherence in writing, making it easier for the reader to follow the writer's argument or narrative.