(In which I make fairly uncontroversial points about evidence using controversial examples, thus providing my own red herring.)
There is a logical fallacy known as appealing to authority, which goes like this.
1. X believes Y
2. X is very clever / a well known expert / a professor / a reliable person …
3. Thus, Y is true
This is a fallacy because people can be wrong, even smart people.
However, we all believe things because someone told us so. We would make impossibly slow progress in life if we had to verify every belief for ourselves. There are people we usually trust – not blindly but because they’ve proven trustworthy.
Modern science has a rather strained relationship with authority. On the one hand, much of science’s early progress came from following the maxim: “don’t believe everything Aristotle said”. If you want to know what the natural world is like, go ask the natural world. Go into the lab, go get a telescope, go find out for yourself. Experiments shouldn’t just be repeatable. They should be repeated.
On the other hand, science has made so much progress, collected so much data, published so many papers that no one person can have checked it all out for themselves. The astronomy preprint archive posts about 100 new astronomy papers per day. We are reliant on the honesty and competence of other scientists who provide us with measurements, constants, equations, simulations. We can check some of it but not all.
The layman is in an even worse position, as they may not have the training, time and skills to verify the conclusions of science even if they wanted to. Should Jo(e) Public believe that the universe is expanding because scientists say so? Or should they build their own telescope, invent the spectrometer, locate and observe distant galaxies, measure atomic emission spectra, calculate the recession velocities of the galaxies, observe Cepheid variable stars, discover their period-magnitude relation, use this relation to measure the distance to galaxies, note the linear dependence of velocity on distance, discover general relativity, solve for an expanding spacetime, derive the linear dependence of velocity on distance, and then (and only then) conclude that the universe is expanding?
The truth, of course, is somewhere in the middle: Jo(e) public can understand how scientists have reached the conclusion that the universe is expanding, so that this central pillar of the Big Bang theory is not pure assertion. They can follow our path on a map, as it were, even if they do not tread every step again themselves. Science ultimately appeals to observations of the natural world, even if they are usually someone else’s observations.
So when should we believe an authority? When does quoting an authority commit the aforementioned fallacy? The key is to be specific about what is being claimed.
Authority as evidence
We mustn’t confuse knowledge with certainty. We need to reason using probabilities. Bayes theorem teaches us how to update our probabilities when new, relevant information comes to light. Learning that a particular expert believes something is new, relevant information. It may not be decisive, but shouldn’t be ignored.
1′. X believes Y
2′. X is in a position to assess the evidence for and against Y. X is informed, competent, experienced, has a reputation for honesty, has no conflict of interest etc.
3′. Thus, the probability of Y being true has increased.
A belief is justified or warranted if it was formed using reliable methods, which can be counted on to produce true beliefs most of the time. Recognising those methods in another person adds weight to their opinion.
Authority as establishing the burden of proof
I really shouldn’t choose such a hot-button topic to make a point like this, but it’s such a good example that I can’t resist. Take climate change. The majority of the climate science community has concluded that the evidence supports the hypothesis that human activity has and will lead to substantial, detrimental changes to our planet’s climate.
Does that prove that climate change is real? No. Proving is something that mathematicians do. It does, however, set the standard for those who believe that climate change is not real. The scientific consensus is prima facie evidence of the truth of climate change. Jo(e) Public is justified, in the absence of the time and skills to investigate for themselves, in believing that climate change is more likely to be true than false. Those who wish to believe that climate change is probably not real have the burden of showing that the scientists are wrong.
This is an application of my last point – authority as evidence. The consensus of an expert, informed community tips the scales in favour of climate change. The pronouncements of scientists are not infallible, but should not be rejected without good scientific reasons. Political conservativism, conspiracy theories and a desire to be viewed as an “iconoclast” are not good reasons.
Authority and Relevance
A key idea in the previous section was relevance. When an climate scientist reaches a conclusion about the state of the Earth’s climate, he is commenting on exactly the thing that s/he studies. There is a danger of experts being viewed as generically clever and thus authorities in any field they care to address. As usual, xkcd summarises the point beautifully.
Another controversial example. I once saw someone on TV (possibly a news vox pop), when asked about life after death, cite as conclusive evidence the fact that Stephen Hawking doesn’t believe that there is life after death. Now, I have every respect for the prodigious talents of Professor Hawking, a scientist about whom the superlative “greatest” justifiably hovers. But none of the things that Hawking has done to gain his reputation have anything to do with life after death. He is an expert on quantum gravity, black holes, general relativity, and the cosmology of the very early universe.
Is there any evidence for life after death? Near death experiences, religious revelation, philosophical (metaphysical) arguments for the immateriality of the soul, and widespread belief in life after death around the world and throughout history are the factors usually cited. So the relevant areas of expertise are medicine, especially neuroscience, as well as a familiarity with the claims of witnesses, the psychology of human beings (e.g. fear of death), philosophy, comparative religion, etc. Life after death is usually taken to be incompatible with philosophical materialism, so philosophical arguments for materialism are also relevant. Prof. Hawking is not an expert in any of these areas. There are, I assume, plenty of doctors, neuroscientists, psychologists and philosophers with the relevant expertise who discount near death experiences and the afterlife. If you want to cite an authority, cite them. Hawking’s opinion in this area is worthy of consideration, of course, but not authoritative.
Beware of 8 out of 10 Authorities
The previous point applies a fortiori to surveys of experts. For example, the fact that a larger-than-average percentage of scientists do not believe in God would seem to explain itself. But there is a possible selection effect. It’s the same selection effect that one may suspect is behind the fact that, while (roughly) 80% of philosophers are atheists, this drops to just 20% of those philosophers who specialise in philosophy of religion.
It’s the same old correlation vs. causation story. Did a random sample enter both fields, and thereafter have their views moulded by their respective subject matter? Or did a prior belief in God lead some to be philosophers of religion, while a lack of belief led others to become scientists? A survey of 1,646 scientists by Rice University sociologist Elaine Howard Ecklund led her to conclude that (from here):
Ecklund concludes from her research that most scientists do not become irreligious as a consequence of their becoming scientists. “Rather, their reasons for unbelief mirror the circumstances in which other Americans find themselves: they were not raised in a religious home; they have had bad experiences with religion; they disapprove of God or see God as too changeable.” The disproportionately high percentage of nonbelievers among scientists (as compared to the general population) would appear to be the result of self-selection: the irreligious seem more likely to become scientists in the first place.
I’m not a sociologist, so I can’t critique Ecklund’s work. The point is that individual biases don’t necessarily average themselves out over a population of experts, so appealing to lots of authorities isn’t necessarily an improvement.
Authority as a counterexample to the accusation of ignorance
The defender of the Kalam cosmological argument for the existence of God claims that the universe has a beginning. One argument goes as follows:
Premise 1. An actual infinite cannot exist in reality.
Premise 2. An infinite temporal regress of events is an actual infinite.
Premise 3. Therefore, an infinite temporal regress of events cannot exist.
Reasoning with actual infinites requires knowledge of mathematics, specifically transfinite arithmetic. The argument’s best known defender is William Lane Craig.Craig is not a mathematician, and so one might wonder whether he is sufficiently familiar with the relevant mathematics. We all know of arguments that reveal more about the ignorance of the arguer than about the subject at hand.
There are two ways for Craig to counter the accusation that a greater knowledge of mathematics would lead one to reject Premise 1. The long way is to demonstrate his own proficiency in transfinite arithmetic. That would take a while. He discusses the topic at length in his book “The Kalam Cosmological Argument” if you want to take that route. There is a shortcut, however. Craig could provide an example of someone whose mathematical credentials are unquestioned and who affirms Premise 1. Craig can do this, and so usually does so in shortened presentations like debates. The authority is David Hilbert, who was one of the greatest mathematicians of the 20th century and who argued that “the actual infinite is nowhere to be found in reality”.
This is a valid appeal to authority, so long as we are clear on what is being claimed. Obviously, we cannot claim that Premise 1 is true because Hilbert thought so. But we can counter the accusation that anyone who believes Premise 1 is ignorant of mathematics and doesn’t understand the idea of infinity.
(Note well: I’m not defending premise 1. I’m planning a series on the cosmological arguments, so stay tuned. I’m not convinced by “Hilbert’s hotel is metaphysically absurd” style arguments. And, as Jeff Shallit has pointed out, mathematical knowledge of transfinite arithmetic is a necessary but not sufficient qualification as we are dealing with the applicability of mathematics to reality, which is physics. The accusation that “greater knowledge of physics / cosmology / relativity would lead one to reject Premise 1” can also be countered: George Ellis. The main utility of these authorities, I contend, is to take our attention away from the claimers and focus attention on the claims. We won’t get stuck in a useless debate about whether Craig really understands maths.).
Authority and hostile witnesses
A particularly useful form of appealing to authority is the use of a hostile witness. In this context, a hostile witness is one who attests to a fact in the teeth of their own biases. If someone who hates the defendant’s guts nevertheless corroborates his alibi, then this has greater weight as evidence than such corroboration from a friend of the defendant. It works in reverse as well: if the defendant’s loving wife testifies that he was out of the house between 10pm and 1am, knowing that this was the time of the murder, then this is weighty evidence. She has every reason to give him an alibi, and so the most likely reason for her statement is that it is true.
This is one of the reasons that the study of history is not paralyzed by the inevitable bias of those who write history. Is the New Testament useless as a historical record, because its writers were followers of Jesus? Not necessarily, because this bias can be used in our favour. If the gospel writers admit something about Jesus that was an embarrassment to them, then we have good reason to believe that they did not invent this story to suit their own ends.
For example, Mark 13:32 has Jesus saying “But about that day or hour no one knows, not even the angels in heaven, nor the Son, but only the Father”. If we can establish that the early Christians believed that Jesus was divine, then there is a strong bias against inventing a saying of Jesus that says that he didn’t know something. It’s not proof, but it is evidence.
As before, we must be clear about the claim that the authority is supporting. A hostile witness can be used to counter the claim that only those biased in favour of a position believe its claims. I’ve come across this in the context of the fine-tuning of the universe for intelligent life. This subject is so popular with theists that I often encounter the claim that it is the product of Christian apologetics, and believed only by “religious types”. Actually, much has been written on fine-tuning in peer-reviewed scientific journals and I can (and have) give many examples of non-theist physicists who affirm that life-permitting universes are rare in the set of possible universes.
But don’t take my word for it …