His Moral Foundations Theory looks at the way morality varies between cultures and identifies five fundamental moral values shared to a greater or lesser degree by different societies and individuals. These are:

1. Care for others, protecting them from harm. (He also referred to this dimension as Harm.)
2. Fairness, Justice, treating others equally.
3. Loyalty to your group, family, nation. (He also referred to this dimension as Ingroup.)
4. Respect for tradition and legitimate authority. (He also referred to this dimension as Authority.)
5. Purity, avoiding disgusting things, foods, actions.

Haidt found that Americans who identified as liberal tend to value care and fairness considerably higher than loyalty, respect, and purity. Self-identified conservative Americans value all five values more equally, though at a lower level than the liberal concern for care and fairness. Both groups gave care the highest over-all weighting, but conservatives valued fairness the lowest, whereas liberals valued purity the lowest. Similar results were found across the political spectrum in other countries.