Mandelbaum was ever wary of being charged with Holism or, more generically, with reification. His wariness was well-founded for his work attracted many such criticisms from Methodological Individualists. In the new millennium, those of us who have built upon his invaluable “collectivist” contributions to develop Critical (or Transcendental or Social) Realism are still assailed by the same charges: that our social ontology and explanatory framework entail reification. In this chapter I will concentrate upon one single paper of Mandelbaum’s, “Psychology and Societal Facts,”1 where my argument will be that he supplies a much stronger defense – indeed the only defense that both Collectivists and Realists can offer to the charge of reification – namely, to insist upon the “activity-dependence” of emergent properties and powers, both in their dia - chronic development and in their synchronic efficacy. In these respects, I will argue that Mandelbaum presented a better defense for the activity-dependence of “societal facts” than for their causal influence being activity-dependent.