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Comment by jjgreen | Hacker News Reader

Do you think? I'd say that axioms were just taken; there's no commitment to their truth (since there is no need for it, and mathematics likes economy).

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Axiom are just taken but over time we picked the most useful ones. This is why they map well to the physical world.

The baffling thing is how few and simple axioms we need for them to be useful.

In math "true" is essentially just a name for a symbol. Saying that an axiom is true is like saying that 3 comes after 2 - it doesn't imply any kind of truth in the usual "consistent with reality" sense.

It also doesn't make sense to define axioms as true. What if later it turns out that the axioms were a mutual contradiction?

Truth is tricky. If I state "The sky is blue", I can look out of the window, the sky is blue, my statement corresponds to the state of the world, my statement is true, right? But in mathematics there is no window, everything is internal, abstract, so what does "truth" mean when there is no state of the world with which to compare? More importantly, would the mathematics be any different if the axioms are declared to be true? No, it wouldn't make any difference at all. So let's leave "truth" to the physicists and philosophers.

That's the first error of the objectivists. Mistaking "blue" as a property of the sky.

Color happens in your head.

That is why trichromacy, tetrachromacy, pentachromacy, dodecachromacy etc. is a thing.

This is perhaps not all that relevant to your point, but "the sky is blue" so often being used as an example of an obvious truth is amusing to me, because very often the sky is not all that blue at all.

If I look outside right now, the sky is probably better described as cyan; quite obviously a different colour from the blue exercise mat that happens to be on my floor.

The sky can also be described by many of the other colours depending on weather or the time of day.

It's almost as if defining anything as a "mathematical truth" is definitionally wrong and anyone having done so should be called out as a liar.

Only the person who responded to the person who made such a statement were more polite about it, hence this "discussion".

This might be a good time to look up the definition of axiom: "a statement accepted as true as the basis for argument or inference".

Yes, but I think that's "accepted" in the sense of "until we run into a contradiction", at which point you have to start over with new axioms. I.e. it turned out your axioms weren't all true.

I think that in the definition you gave "accepted" should be replaced by "assumed".

"John can dig a hole ten feet deep in an hour. How long would it take him to dig a hole five feet deep?"

The first sentence of that problem is an axiom. It is absolutely 100% true, within the context of that story problem. It could contradict another axiom, but it can't turn out to be false, because it's not a statement about the real world.

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