The term “sceptic” comes from the Greek word skeptikos, which means “inquiring”. Scepticism is a method of determining the truth of a claim via rational inquiry. It does not, contrary to popular belief, mean rejecting claims at face value. Scepticism has nothing to do with your conclusion, and everything to do with the method by which you reach your conclusion.

Scepticism is the best method we have for determining the truth of a claim. The scientific method is perhaps the best example of scepticism in action. This method helps prevent us from accepting false claims as true, and from accepting true claims as false.

When evaluating a claim sceptically there are essentially 2 things you should look at:

1. Is it worth evaluating?
2. Does it appear to be true?

Is it worth evaluating?

Not every claim is worth evaluating; some claims can be dismissed immediately. If a claim is internally inconsistent then it can be logically impossible. For example, if I claim “I am 22 years old today and I am not 22 years old today” then you can dismiss that claim right away as it’s simply logically impossible.

Claims can also be dismissed if they lack a quality known as falsifiability. For a claim to be falsifiable, it must make testable predictions that would not be true if the claim were false.  The importance of this attribute is conveyed beautifully in Carl Sagan’s essay “The Dragon In My Garage“, which the claim that an undetectable dragon is living in his garage is evaluated:

Now, what’s the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all?  If there’s no way to disprove my contention, no conceivable experiment that would count against it, what does it mean to say that my dragon exists?  Your inability to invalidate my hypothesis is not at all the same thing as proving it true.  Claims that cannot be tested, assertions immune to disproof are veridically worthless, whatever value they may have in inspiring us or in exciting our sense of wonder.  What I’m asking you to do comes down to believing, in the absence of evidence, on my say-so.

Does it appear to be true?

Once we’ve established that a claim might be correct, the next step is to check whether or not it appears to be correct. In order to do this, we need to look at what would differentiate a universe in which the claim is correct from one in which the claim is incorrect. If a claim is falsifiable, then there must be some difference between the two.

For example, I might suspect that a coin I have in my pocket is weighted such that it lands, when flipped, with the “heads” side up more commonly than it does with the “tails” side up. In order to test this, I would flip the coin.

Suppose that, after flipping the coin twice, both results were heads. Is this enough for me to conclude with any confidence that the coin is weighted? While this result is consistent with my hypothesis, it’s still reasonably likely that a fair coin would land on heads 2 times out of 2 – there’s a 25% chance of this happening to a fair coin – so I can’t really conclude yet that the coin is weighted.

This is important – and I can’t stress this enough – if you don’t have enough information you don’t have to draw a conclusion. It’s okay to say “I don’t know”. In fact, I’d go so far as to say that this is very often the correct thing to say. You should avoid making your mind up about anything until you have enough information to be reasonably confident.

Of course I can’t conclude yet that the coin is not weighted either, as there’s an even greater chance of getting this result for a coin weighted in the way in which I suspect this one to be. Before I can draw a conclusion with any reasonable amount of certainty, I’m going to need to toss the coin quite a few times.

Being able to change your mind when you receive new information is the best definition of open-minded I know. Being closed-minded is refusing to change your mind no matter what evidence you might be given. Being open-minded is re-evaluating claims when new evidence is brought to light, whether that results in a different conclusion or not.

Practicality

Of course, if we were to rigorously examine every claim ever made to us, we’d never have time for anything else. Especially in our daily lives, we need to be able to take some shortcuts, and we don’t always need to demand certainty to the same degree.

Things like trust are often good shortcuts – if we trust someone then we might take their word for something – although for stranger or more important claims it’s still important to be sceptical. Contested claims, also, should generally be examined more sceptically.

When evaluating more important claims like “vaccines cause autism” or “my medicine can cure your cancer”, it is of utmost importance that we examine these claims rigorously. This is what the scientific method, in particular, is great at doing. By incorporating concepts such as controlling and blinding into a scientific test, we can evaluate a claim very rigorously.

There’s one more criteria that should be taken into account for some claims. If a claim is both internally consistent and falsifiable, but disagrees with what we currently think we know, then we need to be much more careful about whether or not we accept it, as accepting such a claim as true also means rejecting a previously accepted claim as false. How consistent a hypothesis is with what we currently know is generally known as the scientific plausibility of a claim.

In order for one idea to supplant another idea of which we are very confident, such as a scientific theory, it needs to make better predictions than the previous idea. For example, Einstein’s theory of general relativity superseded Newtonian gravity after it was shown that the new theory better predicted the orbit of Mercury while remaining consistent with other correct predictions of Newtonian gravity. When this sort of thing happens, the new idea is practically always a variation of the old idea.

Honest Universe

Scepticism is the best tool we have when it comes to forming accurate conclusions about the universe in which we live. It works because, even in its marvellous complexity, our universe is an honest universe.