Moral realism is the view that moral facts are objective and independent of our opinions or cultural beliefs. The moral realist argues that 'murder is wrong' is a statement of the same kind as 'the earth is round'—it is either true or false based on a reality that exists outside of us. Critics of realism, such as moral anti-realists, argue that moral claims are merely expressions of emotion or social conventions. They point to the vast diversity of moral beliefs across cultures as evidence that there is no 'objective' moral truth. Realists respond by noting that disagreement does not prove the absence of truth; people once disagreed about the shape of the earth, but that did not make its shape a matter of opinion.