In recent years, emergentism has resurfaced as a possible method by which to secure autonomous mental causation from within a physicalistic framework. Critics argue, however, that emergentism fails, since emergentism entails that effects have sufficient physical causes, so they cannot also have distinct mental causes. In this paper I argue that this objection may be effective against supervenient emergentism, but it is not established that it is effective against mereological emergentism. In fact, after demonstrating that two founding emergentists, Samuel Alexander and C. Lloyd Morgan, are mereological emergentists, I show how mereological emergentism provides fresh responses to the causal exclusion problem.