Others have added two more categories: "virtue ethics" (in which actions are seen as arising from, manifesting, and giving information about the character of the agent), and "pragmatic ethics" (in which the social context of the action, i.e., the properties of society - its views on, and response to, the act in question).
Given any number of categories, the critical question is then whether, if some of the categories can be shown to be equivalent, that the number could be reduced. Some scholars even suggest that there is only one category: ethical systems.
In any case, we are discussing categories of systems: in each category, there will be many distinct and mutually exclusive systems.
Professor Alfred Freddoso writes that
Important recent work in ethics signals a healthy shift away from "act-centered" moral theories and toward "character-centered" theories. The medievals, of course, fashioned several subtle and interestingly diverse doctrines of virtue, which could perhaps serve as touchstones for contemporary discussions.
Ethics done in this way identifies and enumerates virtues in the agent. Actions manifest or exemplify those virtues, and so remain secondary while virtues are primary in such an ethical system.
