First, some account needs to be given of what counts as an enhancement—an account that must be reasonably intelligible and non-arbitrary, capturing something that might plausibly be thought of as a kind. Second, given such an account, it needs to be shown that it tracks a morally relevant distinction.

Nick Bostrom and Julian Savulescu, Human enhancement ethics: the sate of the debate, in Julian Savulescu and Nick Bostrom (eds.) Human Enhancement, Oxford, 2009, pp. 1–22