To begin with, recall that all ethical theories are either objectivist or relativist. This means that all ethical theories must be committed to one of two things: either they say that there are some ethical evaluations that everyone must recognize as true, or they reject this and say there are no ethical evaluations that everyone must recognize as true. Conventionalism belongs to the latter.
Now, there are lots of different ways you could say that goodness is relative to society or culture. For instance, you might think that you can determine what is good by looking at what is useful for society.
By contrast, you might think that you don’t need to look at what is useful to society to find out what is good, but simply look to what is just accepted by the people of a culture.
As you can see, conventionalism can produce quite different ethical positions. For this reason, conventionalism is a family of theories. All the members of this family say that the good is relative to a specific group, but they can do so in different ways.
Since conventionalism rejects universal ethical truths, it holds that there are no standards that could be used to compare two different societies or cultures.
Since both practices are right within their own cultures, but not across cultures, this shows that conventionalism says that no society or culture is better than any other. They all have the same claim to morality, but only within their own culture. And this shows you that this ethical theory isn’t objectivist.
Many ethical theories don’t suppose there are universal ethical truths, but only conventionalism says that goodness is determined by society or culture. There are many more examples of this. For instance, it is unacceptable to address people in authority with their given or first names in various cultures, but this isn’t the case in others. Also consider the following example.
It should be noted that you can agree that different cultures have different values without committing yourself to conventionalism. You don’t have to say that every culture’s practices are right in order to respect the differences between cultures. You can simply suspend your judgment. Doing so can generate tolerence of difference and help communication and understanding between cultures.
A relativist theory of ethics that maintains that what is good is determined relative to a society, convention, or culture.