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$\sf MM^{++}$ is a 'good' set-theoretic axiom because it is 'Maximum'. Of course, bigger is better. But I'd like to know exactly how the argument works.

Let me be clear about the question posed:

  • What intrinsic and extrinsic justifications do we have to support the claim that $\sf MM^{++}$ is a necessary set-theoretic axiom?

How does $\sf MM^{++}$ clarify the definition of set, what new mathematical results does it bring, and what absoluteness does it bring?


For those who do not understand the history of Martin's Maximum and the differences between the variants, please read the first 8 pages of https://arxiv.org/abs/1906.10213.

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    $\begingroup$ Not being a logician or set theoretician, I don't even know what Martin's Maximum is, but I guess it's some kind of forcing axiom like Martin's Axiom. I never heard anyone claim that MA should be "believed"; I've heard an eminent set theoretician, talking about a result where he used MA, refer to it as "a blatantly false axiom". As far as I know, it's not regarded as any kind of truth, but merely a technical tool for proving consistency results. I guess the case with MM++ (whatever that is) is similar, but I know nothing. $\endgroup$
    – bof
    Commented May 31 at 4:08
  • $\begingroup$ math.utoronto.ca/~stevo/Todorcevic_Structure5.pdf $\endgroup$ Commented May 31 at 13:05
  • $\begingroup$ arpi.unipi.it/retrieve/0b5599b2-ecbd-496e-98d1-ae2a270b5ac2/… $\endgroup$ Commented May 31 at 13:10

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Although it's not really a scholarly publication, the Quanta Magazine article, To Settle Infinity Dispute, a New Law of Logic, gives a good introduction to the topic. That article mentions a conference, Inner Model Theory & Large Cardinals, a 50 year Celebration, but unfortunately I have not been able to find much information about that conference. Another good reference is the 2019 Ph.D. thesis of Jeffrey Schatz, Axiom Selection by Maximization: V = Ultimate L vs Forcing Axioms. In particular, Schatz tries to argue that the "bigger is better" or "maximize" principle favors forcing axioms over V = Ultimate L.

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  • $\begingroup$ Erm, allow me to summarise the defence of $\sf MM$ in the paper. 1. M-fair: an interpretation is "fair" just in case it is a definable inner model of the base theory. 2. M-Max. 3. If UL conjecture + INEC hold, $\sf MM$ strictly M-maxes over UL. 4. $\sf V≠UL$ strictly M-maxes over $\sf V=UL$. 5.$\sf MM$ nor any of its paradigmatic consequences play any direct role in establishing the maximality result. 6. M-Max is not just a justification of $\sf MM$, it can also be a justification of a third route, such as cardinal characteristics of the continuum. 7.Challenges to M-fari itself. $\endgroup$ Commented May 31 at 17:59

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