At least there is only a thing such as ethics to the extent that there is such a thing as the definition of philosophy. And in several senses there is no such thing as the definition of philosophy. First of all philosophy is an idea that we have constructed because we think it is useful. It is not the case that philosophy exists in the world independently of us, and that we are trying to refer to it by its name. If that were the case then there would be a definition for philosophy; the description that best fits what philosophy really is. But that is not the kind of thing that philosophy is. Nor is there a single definition that is properly called the definition of philosophy. We can define philosophy in a number of different ways, and pick whatever definition we like to use. At worst we might disagree about what philosophy is, but neither of us would be wrong (in the sense that it requires an objective standard to compare our use of the term against, of course one of us could be using the word in a way that strays far from the common understanding of it).
I think we are in a similar situation with regard to ethics. Clearly ethics is as much of a constructed idea as philosophy is; when the universe came into existence it isn’t the case that ethics appeared as some distinct feature of the cosmos. No, ethics is an invention of our own for describing and regulating the behavior of people. And similarly there is thus no unique description of what ethics is. Different people may mean different things by ethics, and it may be that neither of them is wrong, they just disagree.
Of course that doesn’t mean that we are free to call anything we wish ethics. There are a few facts which we can take as constraints on what ethics can refer to (derived from common usage and …). First of all ethics must be some set of rules that makes judgments about human behavior. And secondly to call something ethics is to recommend it, which means that the rules called ethical must always be normative, meaning there must always be a reason to follow those rules for the person who is supposed to follow them, even if that reason may occasionally be outweighed by other concerns. (… because if it isn’t always normative it is hard to see why we should care what the theory says we should do.)
Many of the theories called ethical fail these general constraints. Many are only normative some of the time, such as utilitarianism. Utilitarianism is an interesting example, because, if I may digress for a bit, its proponents have a strange conception of what is normative. Utilitarianism is founded on the premise that we have reason to maximize total happiness. Of course we have reason to maximize total happiness some of the time, when it increases our happiness, but there are many times when we have reason to oppose this maximization, when it would make us less happy. Assuming that we don’t desire the maximization of happiness for its own sake (I certainly don’t) then in such cases we don’t have reason to seek the maximization of total happiness. Now of course the proponents of utilitarianism say that the maximization of total happiness is itself a reason to act, even when it is against all of our interests. But when they say this they must mean something other than what you or I mean by the use of the word reason, because for most of us to say that I have reason to do something is to say that it is in my interest to do so, nothing more or less. To start adding other things beyond our interests to that which we have reason to do is unacceptably arbitrary, and opens the door to adding anything we can think of (don’t go outside after 8), which is silly. But I digress; saying such things is only an intellectual exercise, since no one but utilitarians think that utilitarianism in normative, and they will not be convinced to change their minds simply because I call utilitarianism silly or say that it is not actually normative. So think of this instead as an exercise in seeing how a particular theory might be argued to not be ethics proper, by arguing that it isn’t normative, at least not all the time.
But even though many theories fail to satisfy these constraints many others do. The simplest being enlightened self-interest, which advocates the actions that are in our long-term self-interest. Obviously this theory cannot help but be normative. And, similar to it, is a whole family of theories, each of which advocates acting in ways that are beneficial to some group that we belong to. Each of these theories is also always normative, because, although it may advocate acting in ways that are overall detrimental to our wellbeing in some cases, those actions benefit a group we are part of, and thus benefit us to some extent by benefiting the group. So while we always have reason to act in accordance with such theories those reasons may be outweighed by others. And of course there are other theories regulating our actions that are always normative as well, although they are not so easily described, but there is no need to enumerate them here. It is sufficient to point out that there are many theories that may rightly be called ethics. And there isn’t really any further fact of the matter to be had as to which one of them is really ethics. Of course there is plenty of debate to be had still about which theory is best to live by, best to teach to others, and so on. And as a result of such considerations we may decide to call one of them ethics instead of the others. But if we meet someone who uses the term ethics to denote another of these theories, well we can only tell them that we use the word differently, and not that they are wrong.
At this point some readers may be under the impression that I am advocating some kind of extreme relativism regarding ethical facts. But of course that is not the case. Let us say that theories A B and C could all be properly called ethical theories, that we always have reason to act in accordance with their recommendations. Which one of them we actually call ethics doesn’t change that fact at all. Even if we call A ethics we still have reason to act in accordance with theories B and C as well. So the facts themselves, the things that we should and shouldn’t do are fixed. What is relative is which of the theories we call ethical. But that has not impact on the facts, and so, to reiterate, the facts are not relative, only what we call them.
Of course none of this has any impact on our ethical theorizing itself; the content of the theories is the same as it always was. And there is still reason to look for theories that are as “powerfully normative” (usually provide reasons to act that are not overridden by other reasons) as we can make them, without embracing full-blown enlightened self interest, or to look for theories that are as socially or personally useful as possible. The point of all this, really, is to get me out of yet another endless, this-is-what-we-should-call-ethics debate when all the theories on the table are always normative.