In almost any country, you can find someone that holds almost any view. Just think about all the people around you and how they differ in their religious, political, philosophical, and ethical views. Think about how they dress differently, have different taste in art, talk about different things, eat different foods, and have different personalities. To me, all this diversity within a culture is convincing evidence that existing within the same culture does not determine beliefs and behavior.
At the same time, there are easy generalizations we can make about cultures: what sports certain cultures are into, how much certain cultures drink, what religion people in most cultures practice, what political beliefs people in most cultures hold, what kind of clothes people in a given culture count, etc. Obviously, culture influences beliefs and behaviour.
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In epistemological debates, the correlation between beliefs and cultural norms is sometimes brought up as an excuse for skepticism of facts and values. But given the variety of beliefs within a culture, this objection strikes me as a red herring. What’s important isn’t that different cultures have different beliefs; it’s that different people have different beliefs. Bringing the debate to the scale of cultures adds nothing to the argument: that a firm basis for beliefs is required to solve disagreements. The level of epistemological panic one associates with the coexistence of a Jew and a Christian living in the same culture should match the level of epistemological panic one associates with the coexistence of a culture of Jews and a culture of Christians.
Culture obviously influences beliefs but obviously does not determine them. We should think of cultural influence as a strong probabilistic needle, making it likely that certain people hold certain beliefs and behave in certain ways. But the needle does not have a 100% rate of injection.