The standard rule for writing a paragraph is that there is one topic discussed per paragraph. If you change subjects, you must start a new paragraph. Normally, a paragraph will have two or three examples to support the topic sentence. Another element of a paragraph includes analyzing the examples and explaining how or why the examples support the topic sentence. Finally, a paragraph needs to end with a concluding (synthesis) statement that restates the main idea of the paragraph. One main idea=one paragraph. Remember that writing paragraphs is a way to organize your writing so it makes sense to your reader. If you have multiple topics or ideas in the same paragraph, it will be confusing for your reader.