This essay focuses on realism in ontology and on the problem of defining reality. According to the definition given by many realists, reality is independent of our thoughts, conceptual schemes, linguistic practices, etc. Yet, this merely negative definition of reality has some disadvantages: it implies a dualistic view, and it is incompatible with scientific realism. As an alternative, I introduce and discuss the traditional definition of reality as effectiveness, or capability of acting. I then attempt to determine to what extent this definition can be helpful in the debate concerning ontological realism.