“Without science, democracy is impossible,” Bertrand Russell wrote in his foundational 1926 treatise on education and the good life. Three generations later, Carl Sagan (November 9, 1934–December 20, 1996) — another one of our civilization’s most inspired minds and greatest champions of reason — picked up where Russell left off to make an elegant case for the humanizing power of science, its vitality to democracy, and how applying the scientific way of thinking to everyday life refines our intellectual and moral integrity.

In his 1995 masterwork The Demon-Haunted World: Science as a Candle in the Dark (public library) — the source of his indispensable Baloney Detection Kit — Sagan writes:

Avoidable human misery is more often caused not so much by stupidity as by ignorance, particularly our ignorance about ourselves… Whenever our ethnic or national prejudices are aroused, in times of scarcity, during challenges to national self-esteem or nerve, when we agonize about our diminished cosmic place and purpose, or when fanaticism is bubbling up around us — then, habits of thought familiar from ages past reach for the controls.

The true power of science, Sagan suggests, lies not in feeding into our culture’s addiction to simplistic and ready-made answers but in its methodical dedication to asking what Hannah Arendt called the “unanswerable questions” that make us human, then devising tools for testing their proposed answers:

There is much that science doesn’t understand, many mysteries still to be resolved. In a Universe tens of billions of light-years across and some ten or fifteen billion years old, this may be the case forever. […] Science is far from a perfect instrument of knowledge. It’s just the best we have. In this respect, as in many others, it’s like democracy. Science by itself cannot advocate courses of human action, but it can certainly illuminate the possible consequences of alternative courses of action. The scientific way of thinking is at once imaginative and disciplined. This is central to its success. Science invites us to let the facts in, even when they don’t conform to our preconceptions. It counsels us to carry alternative hypotheses in our heads and see which best fit the facts. It urges on us a delicate balance between no-holds-barred openness to new ideas, however heretical, and the most rigorous skeptical scrutiny of everything — new ideas and established wisdom. This kind of thinking is also an essential tool for a democracy in an age of change.

The scientific way of thinking, Sagan asserts, counters our perilous compulsion for certainty with systematic assurance that uncertainty is the only arrow of progress and error the only catalyst of growth:

Humans may crave absolute certainty; they may aspire to it; they may pretend, as partisans of certain religions do, to have attained it. But the history of science — by far the most successful claim to knowledge accessible to humans — teaches that the most we can hope for is successive improvement in our understanding, learning from our mistakes, an asymptotic approach to the Universe, but with the proviso that absolute certainty will always elude us. We will always be mired in error. The most each generation can hope for is to reduce the error bars a little, and to add to the body of data to which error bars apply. The error bar is a pervasive, visible self-assessment of the reliability of our knowledge.

In this continual self-assessment, Sagan argues, lies the singular potency of science as a tool for advancing society:

The reason science works so well is partly that built-in error-correcting machinery. There are no forbidden questions in science, no matters too sensitive or delicate to be probed, no sacred truths. That openness to new ideas, combined with the most rigorous, skeptical scrutiny of all ideas, sifts the wheat from the chaff. It makes no difference how smart, august, or beloved you are. You must prove your case in the face of determined, expert criticism. Diversity and debate are valued. Opinions are encouraged to contend — substantively and in depth. […] Science is part and parcel humility. Scientists do not seek to impose their needs and wants on Nature, but instead humbly interrogate Nature and take seriously what they find. We are aware that revered scientists have been wrong. We understand human imperfection. We insist on independent and — to the extent possible — quantitative verification of proposed tenets of belief. We are constantly prodding, challenging, seeking contradictions or small, persistent residual errors, proposing alternative explanations, encouraging heresy. We give our highest rewards to those who convincingly disprove established beliefs.

Embracing this ethos is an exercise in willingly refining our intellectual and ideological imperfections. Sagan captures this with elegant simplicity:

Valid criticism does you a favor.

He returns to the greatest promise of science as fertilizer for intellectual and spiritual growth, a democratic tool of social change, and a framework for civilizational advancement:

Science is a way to call the bluff of those who only pretend to knowledge. It is a bulwark against mysticism, against superstition, against religion misapplied to where it has no business being. If we’re true to its values, it can tell us when we’re being lied to. It provides a mid-course correction to our mistakes. […] Finding the occasional straw of truth awash in a great ocean of confusion and bamboozle requires vigilance, dedication, and courage. But if we don’t practice these tough habits of thought, we cannot hope to solve the truly serious problems that face us.

Complement the enduringly elevating The Demon-Haunted World with Sagan on science and spirituality, the vital balance between skepticism and openness, his reading list, and this wonderful animated adaptation of his famous Pale Blue Dot monologue, then revisit cosmologist Lisa Randall on the crucial difference in how art, religion, and science explain the universe and Neil deGrasse Tyson’s touching remembrance of Sagan.