In a recent contribution to this journal, C. Sardoni takes issue with the identification by Trigg, in a 2006 publication, of a role for the Keynesian investment multiplier in Marx's schemes of reproduction. Indirectly, Sardoni also expresses his disagreement with Hartwig (by attributing one of his statements to Trigg). We appreciate the opportunity to defend our view against Sardoni's critique. This reply shows that a bridging point between Marx and Keynes can be established without recourse to microfoundations. As suggested by both Trigg, in 2006, and Hartwig, in 2004, the well known Harrod–Domar model of economic growth provides an interpretation of Marx's reproduction schemes that has the Keynesian multiplier as a constituent element. This note will further explore the assumptions underlying the interface between Marx and Keynes, in response to the challenging questions raised in Sardoni's contribution.