The numbers and letters in your MLA outline explain how the ideas relate to each other. The main ideas are represented by capital Roman numerals (I, II) followed by a period, such as "I. Causes" and "II. Effects." Capital letters (A, B) represent the next level under each Roman numeral. The next level of ideas uses Arabic numerals (1, 2), then lowercase letters (a, b) and then numbers inside parentheses. The sections of your outline should remain parallel when possible. If you use an A beneath I, then you must have a B. If you have A, B and C under I, try to create an A, B and C under II. For a final formal outline turned in with your paper, the header should contain small Roman numerals in the header along with your name (Smith i).