"We shall overcome, because the arc of the moral universe is long but it bends toward justice," claimed the Rev. Martin Luther King Jr. on March 31, 1968. A powerful line — it inspired generations of activists, millions of bumper stickers and a few presidents.

Is it true?

I'm not sure what the "moral universe" is. Does it move in an arc? The physical universe moves like a circle. It started with a bang somewhere and continues to head out in all directions for somewhere else. Notions of morality also run in circles. Ideas about right and wrong, let alone the triumph of one over the other, tend to be cyclical.

Theodore Parker, an abolitionist preacher, used the line in 1853: "I do not pretend to understand the moral universe. The arc is a long one. My eye reaches but little ways. I cannot calculate the curve and complete the figure by experience of sight. I can divine it by conscience. And from what I see I am sure it bends toward justice."

Beliefs in a universe bending toward justice are based more in faith than fact. King, at least, had reason for hope: When he invoked the moral universe America had seen the most progress toward racial justice in a century. Five days later he was dead.

Desmond Tutu died last month. An Anglican archbishop, he led the decadeslong fight against apartheid in South Africa, then took on one of the hardest jobs in history: chairing South Africa's Truth and Reconciliation Commission.

It was not about seeking justice; it was about learning to forgive. "You are overwhelmed by the extent of evil," he said. But he also said, "Without forgiveness there is no future." And he said, "Forgiveness means you are given another chance to make a new beginning."

Tutu made the same faith-based claim as his fellow preachers: "This is a moral universe, which means that despite all the evidence that seems to be to the contrary, there is no way that evil and injustice and oppression and lies can have the last word."

I heard him talk once, a tiny man with a high-pitched voice in clerical robes that looked too big for him. He was given to dancing in the aisles and giggling when he was happy, which — against all the odds the universe threw his way — he often was.

Doug Wilhide lives in Minneapolis. He is author of "Nutshells: Diversions in a Time of Pandemic."