This is a crosspost for Does the Arc of History Bend Toward Justice? Outline of an Empirical Test by Eric Schwitzgebel, which was originally published on The Splintered Mind on June 13, 2025. 

Introduction

Overall, on average, do societies improve morally over time? If maybe not in actual behavior, at least in expressed attitudes about right versus wrong?

There's some reason to think so. In many cultures, aggressive warfare was once widely celebrated. Think of all the children named after Alexander the Great. What was he great at? Aggressive warfare is now widely condemned, if still sometimes practiced.

Similarly, slavery is more universally condemned now than in earlier eras. Genocide and mass killing -- apparently celebrated in the historical books of the Bible and considered only a minor blemish on Julius Caesar's record -- are now generally regarded as among the worst of crimes. Women's rights, gay rights, worker's rights, children's rights, civil rights across ethnic and racial lines, the value of self-governance... none are universally practiced, but recognition of their value is more widespread across a variety of world cultures than at many earlier points in history.

An optimistic perspective holds that with increasing education, cross-cultural communication, and a long record of philosophical, ethical, religious, social, and political thought that tests ideas and builds over time, societies slowly bend toward moral truth.

A skeptic might reply: Of course if you accept the mainstream moral views of the current cultural moment, you will tend to regard the mainstream moral views of the current cultural moment as closer to correct than alternative earlier views. That's pretty close to just being an analytic truth. Had you grown up in another time and place, and had you accepted that culture's dominant values, you'd think it's our culture that's off the mark -- whether you embrace ancient Spartan warrior values, the ethos of some particular African hunter-gatherer tribe, Confucian ideals in ancient China, or plantation values in antebellum Virginia. (This is complicated, however, by the perennial human tendency to lament that "kids these days" fall short of some imagined past ideal.)

Random Walk Theory vs Arc of History Theory

With this in mind, consider the Random Walk Theory of value change.

For simplicity, imagine that there are twenty-six parameters on which a culture's values can vary, A to Z, each ranging from -1 to +1. For example, one society might value racial egalitarianism at +.8, treating it as a great ethical good, while another might value it at -.3, believing that one ethically ought to favor one's own race. One society might value sexual purity at +.4, considering it important to avoid "impure" practices, while another might treat purity norms as morally neutral aesthetic preferences, 0.

According to Random Walk Theory, these values shift randomly over time. There is no real moral progress. We simply endorse the values that we happen to endorse after so many random steps. Naturally, we will tend to see other value systems as inferior, but that reflects only conformity to currently prevailing trends.

In contrast, the Arc of History Theory holds that on average -- imperfectly and slowly, over long periods of time -- cultural values tend to change for the better. If the objectively best value set is A = .8, B = -.2, C = 0, etc., over time there will be a general tendency to converge toward those values.

Testing Theories

Each view comes with empirical commitments that could in principle be tested.

On the Arc of History Theory, suppose that the objectively morally correct value for parameter A is +.8. Cultures starting near +.8 should tend to remain nearby; if they stray, it should be temporary. Cultures starting far away -- say at -.6 -- should tend to move toward +.8, probably not all in one leap but slowly over time, with some hiccups and regressions, for example -.6 to -.4 to -.1 to -.2 to +.2.... In general, we should observe magnetic values and directional trends.

In contrast, if the Random Walk Theory is correct, we should see neither magnetic values nor directional trends. No values should be hard to leave; and any trends should be transient and bidirectional, at least between cultures -- and with sufficient time, probably also within cultures. (Within cultures, trends might have some temporary inertia over decades or centuries.)

It would be difficult to do well, but in principle one could attempt a systematic survey of moral values across a wide variety of cultures and long historical spans -- ideally, multiple centuries or millennia. We could then check for magnetism and directionality.

Do sexual purity norms ebb and flow, or has there been a general cross-cultural trend toward relaxation? Once a society values democratic representation, does that value tend to persist, or are democratic norms not sticky in that way? Once a society rejects the worst kinds of racism, is there a ratcheting effect, with further progress and minimal backsliding?

The optimist in me hopes something like the Arc of History is true. The pessimist in me worries that any such hope is merely the naive self-congratulation we should expect from a random walk.