According to our common sense, we know things about the world from ordinary sources such as perception or memory.
Moreover, we assume that what we know about the world doesn’t depend on us thinking about it. The world just is that way.
We also assume that facts about us render us knowledgeable, such as having good reasons to believe something.
Relativism is supposed to challenge our common sense. If what we know turns out to be merely relative to people or cultures, then our common-sense intuitions are all wrong.
Maybe, but we need some kind of relativism that (i) does pose a challenge and (ii) is coherent.
Whether there is such a view will be the topic that follows.
First, some concepts of relativism turn out to be consistent with the common-sense view and thereby don’t contain any challenge to it.
Knowledge relativism is the view that knowledge differs from one person or social group to another or from one time to another. There is nothing in knowledge relativism that is incompatible with our common-sense view. I know more than I used to, people know different things, and societies know other things at different times and locations.
System relativism is the view that knowledge is relative to systems. A system is some mechanism by which we produce beliefs. But this view is also consistent with our common-sense view. My perceptual beliefs are relative to my perceptual system, memories to my memory, and so on.
Justification relativism is also consistent with the common-sense view. People can form rational beliefs but disagree with one another. Being justified in believing something is person-relative. But that doesn’t contradict our common-sense view either.
So far, there have been no genuine challenges to the common-sense view proposed by relativism.
However, there is one more form of relativism to consider. Standards relativism says that there are no universal standards of rationality. Instead, standards are only local to persons or groups.
Such a view does contradict our common-sense intuitions. If there are no universal standards of justification or reason, we can’t explain our knowledge by appealing to them. They aren’t mind-independent facts about us. They are facts about our culture or psychology, and they vary from person to person or culture to culture.
The problem with standards relativism is that it cannot be coherently stated. Consider the following.
“I should adhere to local standards of rationality.”
The standard expressed in the statement is either local or universal. If local, there isn’t any reason for me to hold to it; if universal, it is false.
A relativist may reply that what I take to be epistemic rationality (rationally believing something to be true about the world) is a form of practical rationality (believing something with high utility for life). However, in that case, relativism isn’t relevant to determining what beliefs are epistemically rational. In turn, it isn’t a threatening form of relativism either.
In sum, relativisms of most kinds are compatible with the common-sense view. The only kind that is incompatible is also incoherent. Hence, there is no threat posed by relativism to the common-sense view.
See the relevant chapter in Richard Feldman’s Epistemology for an extended discussion of epistemic relativism.