Still more independence is present in relational holism. This doctrine does not assert top-down control of the whole over its parts, but does claim that the relations of the parts are essential to explanation of behavior of the system. Aristotle and early modern philosophers and scientists tended to describe reality as made of substances and their qualities, and to neglect relations. Gottfried Wilhelm Leibniz showed the bizarre conclusions to which a doctrine of the non-existence of relations led. Twentieth century philosophy has been characterized by the introduction of and emphasis on the importance of relations, whether in symbolic logic, in phenomenology, or in metaphysics.