<p>I’m familiar with the rules on submitting music performance supplements to Yale, not composition supplements, but the general rules are the same. Regardless of the specific submission, it should be conservatory-level. To help your case, your supplement must do more than just demonstrate your passion for and interest in composition; it must demonstrate exceptional talent – that you would be competitive at conservatory.You have said you are not formally trained in composition. I agree with the poster who suggested you start studying composition, if at all possible. At the very least, consult with a professional who can objectively evaluate your composition and help you decide whether it’s conservatory-worthy.</p>