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Comment by adrianN | Hacker News Reader

Prions are nature's grey goo.

I would put bacteria in that role and call them green goo.

One thing I find interesting is that gray goo would have to compete with bacteria for resources. I'm not sure that it would necessarily be easy.

Prions are not alive and therefore do not need to compete for resources to further their existence.

If "not alive" => "doesn't need resources", then "needs resources" => "alive". That doesn't seem right to me.

That's... not how logic works.

I think that might be how logic works. The fallacy seems to be with its parent.

https://en.wikipedia.org/wiki/Contraposition

"Alive implies needs-resources" is not the same as "needs-resources implies alive"

Of course not. And if he'd said "alive implies needs resources", the argument would not be valid.

ianterrelwt posted the article explaining this.

You don't need to hedge. That's exactly how logic works.

That's exactly how logic works.

Yes... it is.

https://en.wikipedia.org/wiki/Contraposition

"All cats die. Socrates is dead. Therefore Socrates is a cat."

No. Mirroring the parent would be : "All cats die. Socrates is immortal. Therefore Socrates is not a cat." Which is perfectly valid logic.

I'll let Eugène Ionesco know.

More like: "Non-living things don't move. The bus moves. Therefore, the bus is alive."

This is false because there exist things that are non-living but move.

Similarly, the original "not alive" => "doesn't need resources" argument is false because there exist things that are not alive that do need resources (such as buses), and so needing resources does not imply being alive.

That's a deductive fallacy. Alive things need resources, but things that need resources are not necessarily alive.

computerphage wasn't using deduction but rather contraposition. (A -> B) => (!B -> !A). The absurdity of (!B -> !A) shows that (A -> B) is not true for all cases.

It's not a fallacy. The truth table for implication and its contrapositive are the same.

    A | B | A => B | ¬B => ¬A
    T | T |   T    |    T
    T | F |   F    |    F
    F | T |   T    |    T
    F | F |   T    |    T

My original point was that my parent was implicitly claiming that only living things need resources. That seemed absurd to me because of things like viruses, companies, governments, etc.

I said, "do not need to compete for resources to further their existence." This is not the same as "do not need resources."

They absolutely compete for resources, in the form of peptides that can fold into more prion aggregates or other proteins

Now that the giant logic thread has played out below I feel I have to point out that I was saying that technological gray goo would have to compete with green goo, I wasn't talking about prions competing for resources.

I have read on Wikipedia that lichens degrade prions, so I disagree with that analogy

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