In this paper, I discuss the question whether objective criteria could be provided for judging something to be a mental illness. I consider the two most prominent objectivist or naturalistic accounts of mental illness, evolutionary and bio-statistical account, which offer such a criterion by relying on the notion of biological function. According to such suggestions, illness is a condition in which there is dysfunciton in some feature of an organism. In this context, I consider different accounts for ascribing functions in (...) biologyand their relationship with the suggested accounts of illnesses. Special focus is placed on the objections according to which the ascription of functions, as envisaged in naturalistic accounts of illness, is incompatible with actual medical and psychiatric practice. I conclude that these objections are legitimate insofar we want to an account of illness that preserves the current practice of ascribing illness. However, the question remains, could a theory that tries to capture the actual medical practice be value-neutral, since our ordinary conception of illness is permeated with value judgments that indirectly enter into medical practice. In that respect, it seems that the requirement for pure objectivity is too strong and thus, it is not reasonable to expect that naturalistic accounts can satisfy it. (shrink)