A parametrised choice principle and Martin's conjecture on Blackwell determinacy Benedict Löwe Abstract: We define a parametrised choice principle PCP which (under the assumption of the Axiom of Blackwell Determinacy) is equivalent to the Axiom of Determinacy. PCP describes the difference between these two axioms and could serve as a means of proving Martin's conjecture on the equivalence of these axioms. Keywords: Blackwell determinacy; Determinacy; Axiom of Choice