Pure moral relativism cannot be categorically true based solely on its own premises.

Caveats

• The strongest academic sources treat the self-refutation objection as a serious but contested challenge, not a decisive refutation — many philosophers defend coherent forms of moral relativism that navigate this paradox.
• The claim's force depends heavily on how 'pure moral relativism' is defined — if it means all truth-apt claims (including meta-level ones) must be relativized, the self-refutation follows, but most relativists do not define their position this way.
• Several sources supporting the claim come from religious apologetics outlets (STR.org, Catholic Answers) with clear ideological commitments against moral relativism, which may overstate the strength of the self-refutation argument.