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Comment by davidivadavid | Hacker News Reader

In what sense are they physical? Can you point to one?

In the sense that they exist in nature. Natural numbers (correctly understood as relations) exist, for example, as atomic valences which permit certain interactions between atoms while preventing others. (This has nothing to do with the Platonism BTW.)

If to you relations exist in nature therefore they are physical, there is a physicalist assumption in there which doesn't go without saying.

Now, I happen to have sympathy for that position, but it's hardly as straightforward as you seem to imply.

Where it does have a lot to do with Platonism is that positing that relations are not abstract things but physical entities presumably entails that you can show what a relation physically is. And an instance of a relation isn't the relation. As soon as you go into "for example", you're not talking about the object itself anymore.

(To better see that relationship, see: https://plato.stanford.edu/entries/abstract-objects/)

So what kind of physical object is a relation?

It pays to draw a distinction between objects and relations. Relations manifest themselves when more than one object is involved. A pair of objects is an object; it is a physical relation between pairs, the isomorphism if you will, that we call "number 2"; it manifests itself in cases when pairs can physically "snap" together solely due to the fact that their cardinalities match. I think it is the fact that a number (a count, in this case) is not tied to a single object (e.g. a pair) but rather expresses the potential of a certain physical interaction between several objects that makes understanding this difficult.

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