While some scholars explain why arguments that limit the scope of discrimination to the classic grounds of race, gender, and so on, are not convincing, none of them establishes a positive argument as to why and when we should consider irrelevant distinctions that are not based on the classic grounds as discrimination. This paper explains why and when arbitrary or irrational distinctions, on their own, constitute discrimination. In a nutshell, the argument is that irrational and arbitrary distinctions are discriminatory, even when they do not relate to classic grounds. This is because, unlike rational distinctions, such as distinctions that are based on reliable proxies, irrational and arbitrary distinctions do not try to treat individuals as autonomous human beings. They ultimately disregard individuals’ relevant needs and capacities. Irrational and arbitrary distinctions thus fail to treat individuals with equal concern and respect.