First, a definition — ethical theory is kind of like a formula for ethical behavior or to make ethical decisions… when you APPLY it to a problem.
There are more or less four kinds of ethical theory — theories that look at consequences, theories that look at motivations, holistic theories that ask ‘what are the elements of being a good person’, and contractual theories.
Consequences: — (or consequentialism) — look at the outcomes of the theory, is the result of the action going to make something “better”. Better can mean either improving a situation by increasing “good” — OR, decreasing “bad”. The most commonly discussed consequentialist theory is utilitarianism. It defines “good” as more or less pleasurable.. so, an action is good if it overall increases pleasure or decreases pain.
To make a decision based on utilitarianism, you simply need to look at all the possible pain and pleasure coming from the action, then do the thing that provides the greatest net increase in good/ decrease in pain. Note, this MAY be different from the ‘greatest good for the greatest number of people’… because, an action may be very good for a small number of people…
What this theory does well is to help a person choose between existing options to do the thing that will do the largest possible net good… so, it tells you which particular action is the best.
Motives — (deontology, Kant.. for the most part) — asks, is the person’s motive or reason for action good. Kant’s reasoning works like this — The only absolutely reliably good thing is a good will — or good motive. He then developed the Categorical Imperative as a test to see if a person’s motive for action (or will.. ) is a good one.
To make a decision based on motives, Kant’s Categorical Imperative requires that, if others knew your motives, they would agree to the action — and, it asks if you would want to live in a world in which others acted as you want to act? This is generally speaking the “universal” formulation of the Categorical Imperative.
Kant continues to give other examples of his Categorical Imperative — one of the really important ones is the means/ ends formulation — which directs you to always treat others as an ends, and never as ONLY a means. Translated, you should not use people to get what you want — you should not withhold information that would make them disagree with the “plan” (i.e. lie to them) — because, what you’re doing is ignoring the fact that they’re an autonomous person (one who has the ability to make decisions about their own life).
You can see how this is a version of the universal formulation — if the action you wanted to take were “universal” — including knowledge of your motives, would that be acceptable?
What Kant’s theory does well is to eliminate possible actions — the problem is that it does not suggest one course of action as the “best”possible thing to do. To narrow down the one course of action among all the permissible ones (the ones that pass the Categorical Imperative), you may use any criteria you’d like.
Holistic theories — The general idea here is to ask what a “good” person does? So — for example, a virtue theory would ask what a good person would do in a particular circumstance? The answer, is that they would be virtuous, and a list of virtuous characteristics would follow. Feminist ethics of care are similar, in that they ask what a good person would do, and the answer centers around making good choices for their family and those in their immediate circle of care.
Contractual — These are theories that are more or less ‘good is what we agree is good’ — kinds of theories. One major kind of contractual theory is the Social Contract theory — in which, whatever the society deems to be ‘good’ IS good. Nothing is good objectively, in that there is nothing about the action itself that can determine what is or isn’t ‘right’.
Another version of the contractual theory are the multitude of professional codes of conduct. So, for example, legal ethics centers on what it means to be a “good” lawyer. That may include NOT breaking a client’s confidentiality if they tell you they’re guilty etc.
Both holistic and contractual theories are often said to be ‘incomplete’, in that they depend on another theory about what is or isn’t right to come to a final decision about the permissibility of an action. On the other hand, they tend to capture how we, as human beings actually DO decide what’s right.