The methodological nonreductionism of contemporary biology opens an interesting discussion on the level of ontology and the philosophy of nature. The theory of emergence (EM), and downward causation (DC) in particular, bring a new set of arguments challenging not only methodological, but also ontological and causal reductionism. This argumentation provides a crucial philosophical foundation for the science/theology dialogue. However, a closer examination shows that proponents of EM do not present a unified and consistent definition of DC. Moreover, they find it (...) difficult to prove that higher-order properties can be causally significant without violating the causal laws that operate at lower physical levels. They also face the problem of circularity and incoherence in their explanation. In our article we show that these problems can be overcome only if DC is understood in terms of formal rather than physical (efficient) causality. This breakdown of causal monism in science opens a way to the retrieval of the fourfold Aristotelian notion of causality. (shrink)