The idea of a two-edged sword, or a sword that cuts both ways, has a storied history. The analogy is somewhat problematic, as swords always have two edges anyway, and it is doubtful that a trained swordsman would  constantly cut himself with his own sword. But regardless, we know what it means. It’s an idea that cuts both for and against its user. It can be difficult to see where ideas and arguments go wrong, but I think it’s vital for a better-informed society that we try to identify and call out bad arguments. This especially applies to ideas that are actually self-defeating – they fail their own criteria.

I think these ideas are more common than we probably realize.

So what makes for a self-defeating idea? Let’s look at 10 examples:

1) All truth is relative.

If all truth is relative, then this statement is also relative, and can’t apply to anything beyond itself. The statement therefore becomes almost meaningless!

2) No one can know the full truth about religion.

This seems like a great and humble statement about religion. Of course it’s arrogant to say you know the full truth about religion, that somehow you have a full and truer view of the world than someone else. So why is it self-defeating? The problem is, that statement is actually claiming a ‘full truth’ about religion. It’s a little like saying there is no such thing as an English sentence.

3) You need for there to be a God.

I’ve heard this before. People think that religious believers need God as a kind of psychological crutch to face the terror of death. Religion, then, is just something made up by people to help them cope. This may be true for some, but this statement is unhelpful, for a couple of different reasons.

First, the origin of a belief doesn’t really have anything to say about the truth value of the belief. Whether I want or need for there to be a God does not usually count as evidence against such a God actually existing. I could have terrible reasons or motives for believing in God (I hope I don’t), but he could still exist.

Second, saying something about someone’s psychological state goes both ways. You say people need there to be a God, I say you need for there not to be a God. Maybe someone doesn’t believe in God because they want to be the master of their fates or don’t want to be held morally accountable for their behaviour. The central point is this: Someone’s needs or desires often having nothing to do with the truth of a particular idea or statement.

The next one’s fun, it’s a pretty popular maxim that I actually found repeated at the start of my logic textbook (how ironic!).

4) “It is wrong, always, everywhere, for anyone to believe anything on insufficient evidence.” – W K Clifford

What evidence is there that we should believe this? The statement fails its own test. There’s no evidence here for that statement being true – therefore we shouldn’t believe this statement.

5) Science is the only reliable guide to truth.

The problem: This isn’t a scientific statement, so we can’t trust that this statement is true! Don’t get me wrong, science is a fantastic tool to help us find truth about the world around us, but it doesn’t answer every question we have about the world around us. Science is primarily empirical – it involves developing theories and testing hypotheses; counting, testing, and examining the world around us – but not everything can be counted or tested by science. The statement above is an example of this.

6) You should doubt or be skeptical of everything.

Therefore I’m doubtful and skeptical of this statement!

7) Many people that grow up in church lose their faith when they go to university and encounter science. God, then, is just an idea for the simple-minded and probably does not exist.

There’s a bunch of different problems with believing this. While some people certainly do stop believing in God for what they see as intellectual reasons when they first attend university, human beings are complex and change their beliefs for a huge variety of different reasons. Further, some become religious during university as well, which immediately casts doubt on this idea.

Regardless, there is a deeper problem here. Correlation is not causation. Just because two things go together, it does not mean one causes the other. Even if low intelligence did correlate with religious belief, that just describes the psychological states of people. It certainly does not mean that God doesn’t exist. The graph below gives a great example of why it’s important to get correlation and causation right. Check out for more amazing but ridiculous correlations.

blog correlation

8) You can’t know anything for sure.

Do you know that for sure?

9) Belief in God is a projection of your culture.

That belief about religion is a projection of your culture. This is similar to 3). Where a belief comes from doesn’t say anything about whether it’s true or not. An ancient pre-scientific tribe may believe the sun sets in the west because that’s what their culture tells them, but that doesn’t mean that they’re wrong!

10) Believing that both naturalism and evolution are true.

This is a bit more indirect, and much more heavily disputed. The key idea is that when these two ideas are combined, you undermine the reliability of how you form beliefs. If the brain and how it thinks have just evolved from fight to survive mechanisms, then we don’t have any reason to suggest the brain comes to true beliefs, just beliefs that are helpful for survival. Therefore, by saying that both naturalism and evolution are true, you undercut the reliability of your cognitive faculties and therefore the reliability of your beliefs. This is a far more complex argument to do justice to within a short paragraph, feel free to hold this one in suspension until I return to it at a later date.

If you’ve believed some of these ideas before, I would encourage you to either refine the way in which you think about the idea or drop it completely. 

I really do think that what we believe changes how we live, and that we should aim to have true beliefs as much as possible. Refusing to believe self-defeating ideas is a fantastic first step.


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