But this is mistaken. Experts can be wrong, and sometimes experts disagree, meaning that at least some (and maybe all) of them are incorrect.
And then there's the danger of hypocrisy: if you accept what an expert says simply because they're an expert, then it would be contradictory to ever disagree with them. Which means you can never disagree with that expert (which is dangerous because, again, even experts are sometimes wrong).
But the central problem with this sort of reasoning is that it isn't valid. Just because someone is an expert about something doesn't mean they are always correct about it, nor does it mean they don't have to defend their assertion with a sound argument.
The Latin name for this fallacy is "argumentum ad verecundiam", or the argument to modesty. The (flawed) idea is that we should be modest in the face of expertise, and simply accept what they say without question.
But everyone has an obligation to provide proof or evidence for what they say, whether they are experts or not.
Ultimately, the only credentials we have is the truth of our assertions and the validity and soundness of our arguments. If you can demonstrate the truth and soundness of what you say, then no further expertise is necessary. But, if you can't demonstrate the truth and soundness of what you say, then you have nothing to support your position, and all the expertise in the world won't salvage it.
It's not enough that an expert says something. They still have to show that there are good reasons supporting the truth of what they say.
EXAMPLES AND ANALYSIS
The author of a new tell-all book about Hillary Clinton could never have seen any of what he claims — he was too low-ranking — say several high-level members of Secret Service presidential details, including the president of the Association of Former Agents of the United States Secret Service.-- From a June 21, 2016, story in Politico by Edward-Isaac Dovere.
On Tuesday, AFAUSSS, which is strictly nonpartisan, is set to release a statement blasting Gary Byrne author of “Crisis in Character,” saying members “strongly denounce” the book, which they add has made security harder by eroding the trust between agents and the people they protect.
“There is no place for any self-moralizing narratives, particularly those with an underlying motive,” reads the statement from the group’s board of directors, which says Byrne has politics and profit on his mind.
Vanessa Oblinger, Byrne’s publicist for the book, said the claim he didn’t witness the events he describes in the book was “a nonsense charge.”
“He was posted directly outside the Oval Office for three years,” she said.
She cited Byrne’s performance awards and positive evaluations, as well as a letter of appreciation he received from the Secret Service in 1996 for his “commitment, dedication and professional performance.”
“The Clintons always trash the messenger,” Oblinger said, adding later, “This is the first of many Clinton-directed media attempts at character assassination.”
Comment: First, what is the importance of AFAUSSS being "nonpartisan"? Is this supposed to make them more credible? Isn't that an appeal to false authority? Second, both the AFAUSSS and Byrne's publicist seem to be making ad hominem arguments: even if it's true that Byrne has some sinister "underlying motive", that doesn't prove anything he's said is false; and even if it's true that the Clintons always "trash the messenger", it doesn't prove that none of their criticisms of Byrne's statements are valid.
COSTELLO: Well, he’s an outsider, and that plays into it, right? Because a lot of Republicans don’t like Sen. John McCain.-- Pundit John Avlon, November 24, 2015, with Carol Costello of CNN. Their remarks concerned the relationship between Sen. John McCain (R-AZ) and Republican political contender Sen. Ted Cruz (R-TX).
AVLON: Unfortunately that is true, in terms of someone who has served his country honorably and was a POW.
Comment: Why is it unfortunate that Republicans wouldn't like McCain? Just because he served in the military and was a prisoner of war doesn't mean anyone has to agree with McCain on anything politically. Are Avlon's remarks questioning the patriotism of McCain's opponents? As a result of serving in the military and being a POW, does McCain have some sort of political authority that we have to recognize?
TEXT: Republicans keep saying the same thing.-- Democratic Party political ad, retrieved November 24, 2015. The ad quotes Republican presidential contenders former Gov. Jeb Bush (R-FL), Ben Carson, Sen. Ted Cruz (R-TX), Sen. Marco Rubio (R-FL), and Donald Trump, as well as former President George W. Bush.
RUBIO: We are at war with radical Islam.
JEB BUSH: Radical Islamic terrorism.
TEXT: Equating Islam, all Muslims, with terrorists…
TRUMP: We do have a problem radical Muslims.
CARSON: Radical Islamic jihadists.
CRUZ: Radical Islamic terrorism.
TEXT: It’s oversimplification. And it’s wrong. But don’t take our word for it.
GEORGE BUSH: We do not fight against Islam, we fight against evil.
GEORGE BUSH: The war against terrorism is not a war against Muslims, nor is it a war against Arabs. It’s a war against evil people who conduct crimes against innocent people.
GEORGE BUSH: That’s not what Islam is all about. Islam is peace.
TEXT: Inciting fear isn’t presidential.
Comment: The ad is accusing Republicans of fear-mongering. It is also falsely accusing Republicans (perhaps via code words?) of equating Islam and Muslims with terrorism and terrorists, thereby demonizing them as bigots. Being opposed to radical Islam doesn't mean being opposed to all Muslims, any more than being opposed to corrupt police officers means being opposed to all police officers. Citing George Bush – a Republican – seems like a faulty appeal to authority, perhaps an argument ad hostes. (Plus, the ad cites George Bush selectively: he denounced Islamic radicalism.)
For those reflexive Trump supporters who believe that he must understand economics because he’s made a lot of money, I ask if you would support George Soros’s economic policy proposals for the same reason.-- Pundit Ross Kaminsky, August 18, 2015. Kaminsky was referring to Republican presidential candidate Donald Trump. Soros is a billionaire whose views on economics are often opposed to Trump's.
Comment: Kaminsky is pointing out that the argument for Trump's expertise is a flawed appeal to authority. In a sense, this is also "comparing" rhetoric: the argument that supports Trump's expertise equally supports Soros' (often opposed) expertise.
"Unfortunately, we’re living through a time in American politics where every foreign policy decision is viewed through a partisan prism, evaluated by headline-grabbing sound bites. And so before the ink was even dry on this deal -- before Congress even read it -- a majority of Republicans declared their virulent opposition. Lobbyists and pundits were suddenly transformed into arm-chair nuclear scientists, disputing the assessments of experts like Secretary Moniz, challenging his findings, offering multiple -- and sometimes contradictory -- arguments about why Congress should reject this deal. But if you repeat these arguments long enough, they can get some traction. So let me address just a few of the arguments that have been made so far in opposition to this deal."-- President Barack Obama, August 5, 2015, speaking on the proposed deal on Iran's nuclear program.
Comment: First, Obama is making it sound as if only opponents of the nuclear deal – and not supporters of it – had made up their minds ahead of time and were viewing the issue through a "partisan prism". That is, Obama is engaging in the "only my opponent" caricature. Second, Obama is making a flawed appeal to authority, dismissing the criticisms of people who aren't nuclear scientists. Just because a person isn't a nuclear expert doesn't mean they have no valid criticisms on nuclear topics. (Some of the criticism of the deal doesn't even rely on nuclear issues, it has to do with diplomatic matters, such as whether Iranian leaders are trustworthy.) Third, Obama says critics are offering "contradictory" arguments, suggesting hypocrisy. But, there's nothing hypocritical about one person offering one criticism, and a different person offering a logically contradictory one. Since Obama doesn't name who the critics are, how do we know they're being hypocritical and self-contradictory? Last, Obama is suggesting something akin to the "big lie" theory is at work with his critics, where repetition of a bad idea will give it credibility.
CHRIS WALLACE: Pope Francis will release an encyclical on the environment... You suggested the holy father should stay out of the debate on climate change...-- Former Sen. Rick Santorum (R-PA), June 7, 2015, during an interview with Chris Wallace of Fox News.
RICK SANTORUM: The Church has gotten it wrong a few times on science. And we probably are better off leaving science to the scientists and focusing on what we do -- what we're really good at, which is -- which is theology and morality.
CHRIS WALLACE: Two points, if he's not a scientist, and, in fact, he has a degree in chemistry, neither are you. That's one point. The second point is, somewhere between 80% and 90% of scientists who have studied this say that humans, men -- human activity, contributes to climate change. so, I guess the question would be, if he shouldn't talk about it, should you?
Comment: Wallace is accusing Santorum of hypocrisy for disqualifying Pope Francis from scientific commentary, but not himself, though he doesn't use it as a basis for an ad hominem argument. Both Wallace and Santorum make an appeal to authority – "scientist should determine what's true in science" – which is flawed reasoning. Whatever the topic, scientists and non-scientists have to abide by the same standards of providing good reasoning behind their beliefs. Scientists shouldn't immediately be believed simply because they are scientists, and the ideas of non-scientists shouldn't immediately be dismissed simply because they are not scientists.
RUSH: Here's Ken in Miami. I'm glad you waited, sir. Great to have you on the program.-- A caller to the Rush Limbaugh show, June 1, 2015.
CALLER: The reason I called was that Republicans were elected to stop Obama. Obama publicly endorsed the USA Freedom Act, so shouldn't that be enough for the Republicans to be against it?
RUSH: Yeah. I feel your pain. The Republicans even acknowledged that they were elected to stop Obama, but then when they have the chance, they don't. Like in the trade deal. This transpacific partnership that still remains a big mystery. It's the Republicans that are gonna pull Obama -- it's caused me to be on the same page as Elizabeth Warren on this. Imagine how bad this thing must be. Actually, Elizabeth Warren's on the same page with me on this thing.
Comment: The caller is saying Republicans have a mandate to stop Obama – or, perhaps, that they have not mandate to NOT stop Obama. The caller also argues that Obama's support for the USA Freedom Act is cause to oppose it, which is something of a reverse appeal to authority (and still invalid reasoning). Limbaugh notes that he agrees with his opponents on the transpacific trade deal, but doesn't seem to use that as an "ad hostes" argument.
Examples from 2012.
Examples from 2009.
"So Senator Obama, who has never traveled south of our border, opposes the Colombia Free Trade Agreement. The same country that's helping us try to stop the flow of drugs into our country that's killing young Americans. And also the country that just freed three Americans that will help us create jobs in America because they will be a market for our goods and products without having to pay -- without us having to pay the billions of dollars -- the billion dollars and more that we've already paid. Free trade with Colombia is something that's a no-brainer. But maybe you ought to travel down there and visit them and maybe you could understand it a lot better."-- GOP presidential candidate Sen. John McCain, October 15th, 2008, during the third presidential debate.
Comment: McCain's admonition to Obama to "travel down there and visit them and maybe you could understand it a lot better" seems like a fallacious argument. Is McCain arguing that, because he's been to Colombia and Obama hasn't, therefore he is right about the trade deal with Colombia and Obama is wrong? If so, then he is making an argument from authority, which is flawed reasoning. After all, there are people who, like McCain, have been to Colombia, but who oppose the trade agreement. Since both sides can't be right, the argument that "whoever went to Colombia is right about the trade deal" is clearly fallacious.
"We cannot impose a military solution on what has effectively become a civil war. And, until we acknowledge that reality, we can send 15,000 more troops, 20,000 more troops, 30,000 more troops, I don't know any expert on the region or any military officer that I've spoken to privately, that believes that that is going to make a substantial difference on the situation on the ground."-- Sen. Barack Obama (D-IL), January 14, 2007, on Face the Nation:
Comment: President George W. Bush announced the Iraq "surge" in January 2007, which involved sending more troops to Iraq. By October 2007, violence in Iraq had dropped significantly, and continued to decline through 2008. How much of a role the surge played in decreasing the violence is certainly debatable, but it seems like it made a substantial difference on the ground. In any event, Obama must do more than just cite experts, he must show that the experts have good reasons behind what they say.
(The list above is not intended to be a comprehensive record of all relevant examples.)