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In this first image, Ernie Bushmiller’s character Sluggo (from his classic strip Nancy) is dreaming of himself dreaming of himself dreaming of himself, without end. It is clearly a case of self-reference, but it involves an infinite regress, analogous to a PM formula that contained its own Gödel number directly. Such a formula, unfortunately, would have to be infinitely long!

Our second image, in contrast, is the famous label of a Morton Salt box, which shows a girl holding a box of Morton Salt. You may think you smell infinite regress once again, but if so, you are fooling yourself! The girl’s arm is covering up the critical spot where the regress would occur. If you were to ask the girl to (please) hand you her salt box so that you could actually see the infinite regress on its label, you would wind up disappointed, for the label on that box would show her holding a yet smaller box with her arm once again blocking the regress.

And yet we still have a self-referential picture, because customers in the grocery store understand that the little box shown on the label is the same as the big box they are holding. How do they arrive at this conclusion? By using analogy. To be specific, not only do they have the large box in their own hands, but they can see the little box the girl is holding, and the two boxes have a lot in common (their cylindrical shape, their dark-blue color, their white caps at both ends); and in case that’s not enough, they can also see salt spilling out of the little one. These pieces of evidence suffice to convince everyone that the little box and the large box are identical, and there you have it: self-reference without infinite regress!

In closing this chapter, I wish to point out explicitly that the most concise English translations of Gödel’s formula and its cousins employ the word “I” (“I am not provable in PM ”; “I am not a PM theorem”). This is not a coincidence. Indeed, this informal, almost sloppy-seeming use of the singular first-person pronoun affords us our first glimpse of the profound connection between Gödel’s austere mathematical strange loop and the very human notion of a conscious self.

CHAPTER 11

How Analogy Makes Meaning

The Double Aboutness of Formulas in PM

IMAGINE the bewilderment of newly knighted Lord Russell when a young Austrian Turk named “Kurt” declared in print that Principia Mathematica, that formidable intellectual fortress so painstakingly erected as a bastion against the horrid scourge of self-referentiality, was in fact riddled through and through with formulas allegedly stating all sorts of absurd and incomprehensible things about themselves. How could such an outrage ever have been allowed to take place? How could vacuously twittering self-referential propositions have managed to sneak through the thick ramparts of the beautiful and timeless Theory of Ramified Types? This upstart Austrian sorcerer had surely cast some sort of evil spell, but by what means had he wrought his wretched deed?

The answer is that in his classic article — “On Formally Undecidable Propositions of Principia Mathematica and Related Systems (I)” — Gödel had re-analyzed the notion of meaning and had concluded that what a formula of PM meant was not so simple — not so unambiguous — as Russell had thought. To be fair, Russell himself had always insisted that PM’s strange-looking long formulas had no intrinsic meaning. Indeed, since the theorems of PM were churned out by formal rules that paid no attention to meaning, Russell often said the whole work was just an array of meaningless marks (and as you saw at the end of Chapter 9, the pages of Principia Mathematica often look more like some exotic artwork than like a work of math).