  The connection between emergence and simulation was perhaps best articulated by Bedau in his (2011). Bedau argued that any conception of emergence must meet the twin hallmarks of explaining how the whole depends on its parts and how the whole is independent of its parts. He argues that philosophers often focus on what he calls “strong” emergence, which posits brute downward causation that is irreducible in principle. But he argues that this is a mistake. He focuses instead  on what he calls “weak” emergence, which allows for reducibility of wholes to parts in principle but not in practice. Systems that produce emergent properties are mere mechanisms, but the mechanisms are very complex (they have very many independently interacting parts). As a result, there is no way to figure out exactly what will happen given a specific set of initial and boundary conditions, except to “crawl the causal web”. It is here that the connection to computer simulation arises. Weakly emergent properties are characteristic of complex systems in nature. And it is also characteristic of complex computer simulations that there is no way to predict what they will do except to let them run. Weak emergence explains, according to Bedau, why computer simulations play a central role in the science of complex systems. The best way to understand and predict how real complex systems behave is to simulate them by crawling the micro-causal web, and see what happens.