A great truth is a truth whose opposite is also a truth.

Mann’s aphorism points to a paradoxical feature of profound ideas: they often illuminate reality from more than one angle, so that an apparent contradiction can also contain validity. “Great truth” here suggests not a simple factual statement but a deep insight about human life, ethics, art, or politics—domains where competing principles (freedom and order, individuality and community, reason and passion) can each be “true” within their own limits. The line cautions against dogmatism and invites dialectical thinking: mature understanding holds tensions rather than resolving them into slogans. It also implies that lesser “truths” are one-sided—statements whose negation is plainly false—whereas the greatest insights are complex enough to make room for their opposites.