It is suggested in this article, in response to claims made by John Murphy in a previous article in this journal, that there is an important role to be played by philosophical and constitutional arguments in the debate concerning the possible legal recognition of same-sex marriage. Murphy's claim, that a purely 'legalistic' approach based on European Convention case-law is enough to make out the case for same-sex marriage, is insufficient either to make that case or to explain how courts have in fact been deciding cases since the Human Rights Act 1998 came into force. Those who are concerned to present a plausible case for the legal recognition of same-sex marriage must, and inevitably do, take their arguments beyond the purely 'legalistic' level. Arguments for legal recognition will be gravely weakened unless this point is recognised.