The main idea is the central message that an author intends to convey in the individual and collective parts of a written work. Each paragraph has a main idea, and these individual segments work together to support the main idea of a story or essay as a whole.
When writing a paragraph, an author uses a topic sentence to describe what the paragraph discusses. The topic is expanded by including supportive details, and these two elements jointly communicate the main idea. For example, in a grant letter asking for donations to update a neighborhood recreation center, the writer may include information about park safety hazards and statistics about crime rates in neighborhoods without community outreach. This supportive information helps convey the main idea that providing a safe recreation site can improve the long-term well-being of neighborhood children.