Naturalism is a cluster concept, like religion or realism, and similarly vague. There is no single defining characteristic of religion, only a collection of imprecise conditions that overlap or even conflict with one another. Something is a religion if it has many of those characteristics, but no condition is either necessary or sufficient. For example, most (but not all) religions have a supreme being; most (but not all) claim the supreme being is the creator of all things and has a personal interest in each of us; most (but not all) provide a moral code that guides our behaviour; most (but not all) call for worship and ritual performance on a regular basis; most (but not all) have a special class of people (gurus, mullahs, priests, rabbis) who interpret the religion to others; and so on. Some of the most important concepts in philosophy and daily life are like this: democracy, or a dignified death, for example. We spend at least as much time arguing about the nature of the concept of democracy as we do about the proposition that it is or isn't a good thing.