As we saw in the Introduction, the term "nature' has several meanings. According to a long-standing tradition, it denotes the part of reality that is material rather than soul- or mind-like, res extensa as opposed to res cogitans. On this dualistic conception, human beings are thought to be partly natural (on account of their having bodies) and partly non-natural (on account of their having souls or minds). So although a man has a certain size, shape and mass, he is thought also to possess a radically non-natural part, a soul or a mind.