when a paragraph develops one key by controlling idea, we say the paragraph has
4.1 Characteristics of Effective Paragraphs. 4.1.1 Unity. A paragraph with unity develops one, and only one, key controlling idea, to ensure unity, edit out any stray ideas that donât belong and fight the urge to take interesting but irrelevant side trips; they only create confusion about your destination. 4.1.2 The Topic Sentence.