In today’s world, skepticism is more important than ever before.

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Last week, noted economist and public figure Paul Krugman wrote an opinion piece for the New York Times. Called “Imaginary Health Care Horrors,” it details the current (Republican) drive to cancel the Affordable Care Act / Obamacare / National Romneycare / not-quite-as-good-as-Universal Healthcare that seems, by all accounts save congressional Republican ones, to be going pretty well, bringing coverage to millions, at 20% under budget. But what he’s really writing about is the insistence, despite all contrary evidence, that Obamacare is a failure. And he coined a term: “post-truth politics.” I think we can expand that to the Post-Truth World.

The Post-Truth World is one in which public figures cherry pick from available data to make untrue claims true, thereby devaluing the very nature of truth. It’s a world in which oil companies use the same deceitful tactics to “disprove” global warming that the tobacco industry used to “disprove” the link between smoking and lung cancer. It’s a world in which anti-vaccine activists still cite studies that are very well known to be discredited, and 9/11 (or Benghazi) “truthers” or so-called “birthers” entirely discount all the evidence against their tinfoil hat theories because the data are all lies anyway.

The Post-Truth World is why we need skepticism. It’s why we need skeptics.

Part of it is a problem with rhetoric.

The concept of truth is a slippery one, because scientists don’t deal in truth. They deal in hypothesis and evaluation, in theory and consensus. Off the record, a climate scientists will tell you, 97.2% of the time, that humans are the cause of the very real climate change that is taking place on Earth. On the record, they will only tell you that it is “very likely” the case, and that the data fit the hypothesis better than any other currently-proposed explanation. But Ted Cruz will tell you that “the last 15 years, there has been no recorded warming. Contrary to all the theories that – that they are expounding, there should have been warming over the last 15 years. It hasn’t happened.” He is certain (also: wrong), but worse than that, he’s certain in public. On the record.

Another part of it is a problem with authority.

A lot of people don’t seem to view scientists as authorities anymore. There’s a lot of respect for “science” and what it’s done for us, but not for the views espoused by the experts, the scientists themselves. When it comes to some of the most important issues of our time, many of us seem just as likely to believe a politician as a scientist about global warming being caused by humans (yes, 54% of Americans is a serious improvement, but that’s still only about half when the scientific consensus is 97%). Some people even believe celebrities over scientists, too, often to detrimental effects.

Enter skepticism.

Skepticism isn’t (as climate change deniers might have one believe) just going against the prevailing consensus. When Ted Cruz uses the word “skeptic” to describe his views on climate change, and then compares himself to Galileo for going against the mainstream views, he’s fundamentally misunderstanding what skepticism means.

Skepticism is withholding judgement until provided with a preponderance of evidence. It’s also changing one’s opinion when presented with verifiable data that contradict one’s views. It’s as much about agreeing with the consensus when the data support it as disagreeing with it when the data do not. Galileo had data that showed geocentrism to be false; Ted Cruz has only his own opinion.

Skepticism is the application of a scientific worldview. You can do it even if you’re not a scientist: I’m a literary historian for crying out loud. Skepticism just entails personal research, patience, and, very importantly, an understanding that experts know more about their field of study than you do.

The Post-Truth World treats all expertise as equal, and a skeptic knows that’s not the case.

If you’re, say, a plumber, and someone tells you that a pipe to the street should be buried at a certain depth (and they’re wrong), you’re going to be a little ticked off. That’s the way a climate scientist is going to feel when a plumber tells her global warming isn’t real. That’s the way a doctor is going to feel when an actor says vaccines cause autism. We don’t have to automatically believe a scientist just because he or she is a scientist, either — a geologist isn’t going to know much more about vaccines than a doctor would about global warming. A TV-producer, though most likely quite knowledgeable about producing television programs, isn’t likely to be an expert on cosmology. In cases where the expertise doesn’t fit the claims being made, there’s no reason to give it any special weight. But expertise in the relevant area? That matters. It doesn’t make them always right, but it makes them worth listening to. At least more than a politician speaking about anything other than politics.

And that’s why we need more skeptics: because in the Post-Truth World, relevant experts are often replaced with irrelevant talking heads. Because not all expertise is created equal. Because the experts are almost never “certain in public.”

And maybe someone still needs to be.

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Richard Ford Burley is a doctoral candidate in English at Boston College, where he’s writing about remix culture and the processes that generate texts in the Middle Ages and on the internet. In his spare time he writes about science and skepticism here at This Week In Tomorrow.