David Foster Wallace famously argued that “learning how to think really means learning how to exercise some control over how and what you think.” Yet in an age of ceaseless sensationalism, pseudoscience, and a relentless race for shortcuts, quick answers, and silver bullets, knowing what to think seems increasingly challenging. We come up with tools like The Baloney Detection Kit and create wonderful animations to teach kids about critical thinking, but the art of thinking critically is a habit that requires careful and consistent cultivation. In his remarkable essay titled “The Burden of Skepticism,” originally published in the Fall 1987 issue of Skeptical Inquirer, Carl Sagan (November 9, 1934–December 20, 1996) — always the articulate and passionate explainer — captured the duality and osmotic balance of critical thinking beautifully:

It seems to me what is called for is an exquisite balance between two conflicting needs: the most skeptical scrutiny of all hypotheses that are served up to us and at the same time a great openness to new ideas. Obviously those two modes of thought are in some tension. But if you are able to exercise only one of these modes, whichever one it is, you’re in deep trouble.

If you are only skeptical, then no new ideas make it through to you. You never learn anything new. You become a crotchety old person convinced that nonsense is ruling the world. (There is, of course, much data to support you.) But every now and then, maybe once in a hundred cases, a new idea turns out to be on the mark, valid and wonderful. If you are too much in the habit of being skeptical about everything, you are going to miss or resent it, and either way you will be standing in the way of understanding and progress.

On the other hand, if you are open to the point of gullibility and have not an ounce of skeptical sense in you, then you cannot distinguish the useful as from the worthless ones. If all ideas have equal validity then you are lost, because then, it seems to me, no ideas have any validity at all.

Some ideas are better than others. The machinery for distinguishing them is an essential tool in dealing with the world and especially in dealing with the future. And it is precisely the mix of these two modes of thought that is central to the success of science.