How do we know anything at all?

The other day I saw someone shared a post saying: ‘I don’t know if the world is a sphere or not and neither do you because neither of us has seen it from space.’


It occurred to me it might be a good idea to talk about how we know anything at all?

Here are three things that I hope you all know.

1. Fires are hot
2. Jumping out of a plane without a parachute is fatal.
3. Tunisia is a country in North Africa.

But how we do know these things are true?

In the case of fire you have experience of it being hot. You’ve felt it (hopefully without getting too badly burned). Your senses told you. True, it could have been a hallucination but that would have to be a pretty reliable hallucination to make every fire you’ve ever encountered hot.

How about jumping out of a plane without a parachute?

You haven’t done it and you probably don’t know anyone who’s done it. Yet you can be quite confident that while you might have some interesting spiritual insights on the way down you probably won’t get to share them with anyone. In this life anyway.

How do you know that?

You use reason. You know that soft, heavy things like human bodies go squish when they hit hard things like the ground at high speeds. You’ve seen what happens to an egg when it’s dropped on the floor. It makes sense.

How about Tunisia? Only a small percentage of the people reading this will have been there but I imagine that most of you believe it exists?

But why?

Presumably because it’s on every map. Geographers and cartographers presumably know what they’re doing. And politicians and journalists also seem to agree that Tunisia exists.

But if next week there springs up a Tunisia Truther movement that claims that bit of North Africa isn’t really a country but a hideaway for Michael Jackson, Elvis Presley and a few surviving Nazis…would you think again?

For most of us, we accept that Tunisia the same way that we accept that water is made up of two hydrogen particles and one oxygen particle (H2O) – we trust the experts to tell us the truth. We outsource our knowledge.

So we can know things through our senses. We can know things by working them out. And we can know things by other people working them out for us. Often we combine all three.

But can we know anything for certain?

No. We can’t really be certain about anything. That’s just part of being alive. But that’s not the same as saying we can’t know things.

Think for a moment about your best friend. How can you be sure that they’re not actually a government spy keeping tabs on you?

Sure, you’ve known them for years, maybe you know their family, too, they seem so genuine. But wouldn’t a really good spy be able to fake all that?

Seems pretty unlikely, right? Not impossible but just so unlikely that it’s not worth really considering.

Likewise when I put bread in the toaster I assume it’s the heating element inside that turns it into toast. It could be pixies but it doesn’t seem probable.

This is actually another way that we can know things. We can rule out the really unlikely unless some amazing bit of evidence comes along to change our minds.

In fact, that’s a rule of thumb in science: extraordinary claims need extraordinary evidence.

So when someone tells you that you can’t know something for sure, it’s technically true…but also basically meaningless. We don’t need perfect certainty to know how the world works. Using our senses, our reason and what experts tell us, we can drive our cars, feed our children and brush our teeth and be confident that we’re doing it right.

We can’t be certain but 99.99% of the time it isn’t pixies.


Further reading: – some great animations on the nature and history of epistemology – on the limits of what we can know and how when it comes to down to it we don’t know anything at all with certainty