In his new book, "Rationality," Steve Pinker ends with a Why Rationality Matters chapter. Here's some excerpts.
Pinker starts off by looking at human progress.
Though the availability bias hides it from us, human progress is an empirical fact. When we look beyond the headlines to the trend lines, we find that humanity overall is healthier, richer, longer-lived, better fed, better educated, and safer from war, murder, and accidents than in decades and centuries past.
Having documented these changes in two books, I'm often asked whether I "believe in progress." The answer is no. Like the humorist Fran Lebowitz, I don't believe in anything you have to believe in.
Though many measures of human well-being, when plotted over time, show a gratifying increase (though not always or everywhere), it's not because of some force or dialectic or evolutionary law that lifts us ever upward.
On the contrary, nature has no regard for our well-being, and often, as with pandemics and natural disasters, it looks as if its trying to grind us down. "Progress" is shorthand for a set of pushbacks and victories wrung out of an unforgiving universe, and is a phenomenon that needs to be explained.
The explanation is rationality.
When humans set themselves the goal of improving the welfare of their fellows (as opposed to other dubious pursuits like glory or redemption), and they apply their ingenuity in institutions that pool it with others', they occasionally succeed.
When they retain the successes and take note of the failures, the benefits can accumulate, and we call the big picture progress.
...Brainchildren of human ingenuity have also underwritten other historical boosts in well-being [in addition to life expectancy, marked lessening of hunger, poverty, and deaths from war], such as safety, leisure, travel, and access to art and entertainment.
Though many of the gadgets and bureaucracies grew organically and were perfected through trial and error, none was an accident. People at the time advocated for them with arguments driven by logic and evidence, costs and benefits, cause and effect, and tradeoffs between individual advantage and the common good.
Pinker then turns to how rationality leads to moral progress.
Progress consists of more than gains in safety and material well-being. It consists also in gains of how we treat each other: in equality, benevolence, and rights.
Many cruel and unjust practices have declined over the course of history. They include human sacrifice, slavery, despotism, blood sports, eunuchism, harems, foot-binding, sadistic corporal and capital punishments, the persecution of heretics and dissidents, and the oppression of women and of religious, racial, ethnic, and sexual minorities.
None has been extirpated from the face of the earth, but when we chart the historical changes, in every case we see descents and, in some cases, plunges. How did we come to enjoy this progress?
...A popular view is that moral progress is advanced through struggle: the powerful never hand over their privileges, which must be wrested from them by the might of people acting in solidarity.
My greatest surprise in making sense of moral progress is how many times in history the first domino was a reasoned argument.
A philosopher wrote a brief which laid out arguments on why some practice was indefensible, or irrational, or inconsistent with values that everyone claimed to hold. The pamphlet or manifesto went viral, was translated into other languages, was debated in pubs and salons and coffeehouses, and then influenced leaders, legislators, and popular opinion.
Eventually the conclusion was absorbed into the conventional wisdom and common decency of a society, erasing the tracks of the arguments that brought it there.
Few people today feel the need, or could muster the ability, to formulate a coherent argument on why slavery is wrong, or public disembowelment, or the beating of children; it's just obvious. Yet exactly those debates took place centuries ago.
And the arguments that prevailed, when they are brought to our attention today, continue to ring true. They appeal to a sense of reason that transcends the centuries, because they conform to principles of conceptual consistency that are part of reality itself.
Now, as we saw in chapter 2, no logical argument can establish a moral claim. But an argument can establish that a claim under debate is inconsistent with another claim a person holds dear, or with values like life and happiness that most people claim for themselves and would agree are legitimate desires of everyone else.
As we saw in chapter 3, inconsistency is fatal to reasoning: a set of beliefs that includes a contradiction can be deployed to deduce anything and is perfectly useless.
...The power of rationality to guide moral progress is of a piece with its power to guide material progress and wise choices in our lives. Our ability to eke increments of well-being out of a pitiless cosmos and to be good to others despite our flawed nature depends on grasping impartial principles that transcend our parochial experience.
We are a species that has been endowed with an elementary faculty of reason and that has discovered formulas and institutions that magnify its scope. They awaken us to ideas and expose us to realities that confound our intuitions but are true for all that.