Forget for a second whether or not this particular video is ok. (I wouldn’t show it to my students; you never knows what someone is dealing with.) But doesn’t this say something about mathematical culture? What are we training mathematical people to ignore?

]]>A cute book that is actually terrifying and may actually be a deep critique of math. pic.twitter.com/PsAaqFr3h5

— Michael Pershan (@mpershan) March 8, 2019

This is a book that I first read when I was 18 and studying in yeshiva in Israel. But I didn’t really read it very well back then. This is for two reasons. First, I wasn’t sleeping well at all, and I read Grade’s novel only between the hours of 11 and 1. Second, I was a ball of anxieties about secular/religious tensions, and ill-equipped to make sense of the world of ideas Grade was constructing.

In Yiddish the novel is called *Tzemach Atlas*, and we are quickly introduced to the man himself. Tzemach Atlas is an extreme adherent of the Navarodok branch of the musar movement. He believes that man’s desires need to be entirely uprooted through extreme self-reflection. He can find the flaws and hypocrisies in both common people as well of in great rabbis. He obsesses constantly over his own faults, and has gained a reputation as a brave teacher who is willing to “save” his students for the yeshiva. And yet, on the very first page, we are told that he is haunted by his doubts about the existence of God.

Then a lot of things happen — I won’t burden you with them all! — but we’re eventually introduced to Chaikl Vilner, i.e. Graim Chade, i.e. this is just a stand-in for the author Chaim Grade himself.

Tzemach Atlas eventually takes Chaikl into his upstart musar yeshiva. (Chaim Grade himself spent time studying in a Navarodok musar yeshiva.) Misery ensues for everyone involved, especially Tzemach Atlas and Chaikl.

And then, in the last fifth of the novel, the great *gaon *and Talmudic scholar Rabbi Avraham-Shaye shows up, vacationing in the small town where the yeshiva is. He takes a liking to Chaikl and invites him to be his personal study partner — this is shocking, as it is wildly unlike a great Torah scholar to take a young study partner.

Amazingly, though, all of this is more or less true. Rabbi Avraham-Shaye is a stand-in for Rabbi Avrohom Yeshaya Karelitz, who published under the pseudonym “Hazon Ish.” Chaim Grade was his study partner for many years.

I’m rereading the book now — I just finished Volume 1, and am ready to start Volume 2 — and the biggest surprise for me has been just how clearly Grade sides with Karelitz. Grade himself left the religious life and fell in with the secular Vilna Circle. Nevertheless, his portrait of Karelitz is almost hagiographical — it’s beaming and admiring.

Though it’s reductive to put it like this, it seems to me as if Grade wanted to write this book simply to take his teacher’s side in an argument about the value of musar.

The real Karelitz was a critic of musar and its ability to improve a person’s character. As Lawrence Kaplan writes in a piece about Karelitz’s views, the *musarniks *had the whole thing backwards:

The Hazon Ish was of the opinion that the fundamental Musar approach of working on oneself, of turning inward, in order to develop one’s spiritual personality and overcome the obstacles standing in the way of proper observance was fundamentally misguided.

In the novel, Tzemach Atlas, the great man of musar*, *slowly comes apart at the seams. He is a failure in every single aspect of his life. He is unable to keep a “proper” engagement, and runs off with a wealthy secular woman. And though he shows moments of clear moral insight — and impresses his wife with his clarity and moral standards — he alienates himself from an entire town. He then runs off to start his own yeshiva, and finds that he is unable to influence his students in the least.

But from the perspective of the novel, this is wholly due to his own faulty ideology and personality. When Chaikl starts spending the night with a local girl (bad Chaikl!) Atlas reprimands him, but succeeds only in inciting Chaikl’s rage.

In contrast is the positive influence of Rabbi Avraham-Shaye. He is even able to influence the child Melechke, who goes about bragging about every little accomplishment for the first 330 pages of the novel. I don’t want to go too hard on him — he’s just 11! — but really he’s a greedy, sniveling braggart who annoys everyone.

But after he visits Avraham-Shaye? He’s a changed boy!:

As soon as the visitor and his escorts withdrew, the younger students surrounded Melechke. Although he had grown and matured somewhat and could already read a chapter of the Talmud, Melechke was still considered a spoiled only child and a show-off who trust himself into the midst of older people so they would test him in Talmud and pet him. His friends couldn’t understand why he hadn’t told them that he had visited Reb Avraham-Shaye.

“I went to see Reb Avraham-Shaye Kosover to discuss Torah with him,” Melechke replied, “and I probably asked him about a dozen questions about the first page of the Tractate

Kiddushin. So Reb Avraham-Shaye told me, ‘Come into my house and we’ll open my copy of theKiddushinand look at that matter together. Then you cn ask what you have to ask.’ So we studied the page together, and all my questions were answered of their own accord. When we left his room, Reb Avraham-Shaye led me to the low window which faced the forest and told me, ‘Climb out. Let’s see if you can climb out of a window as nimbly and quickly as you can ask questions.'” Melechke spread his hands like an old Torah scholar and concluded, “Since I didn’t hear any new interpretations from him, what was there to tel you? How I crawled out the window in the woods, and how he crawled out after me?”

Later, once Chaikl is invited to be the personal study partner of the great *gaon*, he finds himself unable to remain the night with his landlady’s daughter:

“How could he look Reb Avraham-Shaye straight in the eye and debate lofty matters with him when he did such improper things at night? His shame at deceiving a saintly gaon changed to fear: Perhaps Reb Avraham-Shaye knew? A man like that had divine intuition…”

Later, when the gaon debates Tzemach Atlas in the closing pages of the book, Avraham-Shaye makes the case that through studying the Talmud and its commentaries one essentially gains moral influencers along these lines: “A youngster pores over his Talmud in Vilna and muses that he’s in Babylonia, sitting in the great Talmudic academy of Nahardea, in the beth medresh of Rashi and his scholarly descendants.” So, through Torah study one obtains moral exemplars who effect a profound moral influence. (Or maybe it’s Torah itself that exerts the influence?) Greater than whatever results from the intense moral introspection and trials that the mussarniks recommend.

Two things seem remarkable about this to me. First, that this is essentially the *actual *view of Karelitz. Second, Chaim Grade seems to have written this novel so as to adopt this perspective wholeheartedly. In the final lines of this book, Tzemach Atlas walks away a broken man, having been absolutely seen-through by the visiting gaon.

There is one place, however, where Grade seems to go beyond his teacher. Late in the book, with nowhere else to go, Chaikl goes to the beautiful wooden shul to sit alone. (Sidenote: the wooden shuls of Poland really are a wonder.) He sits there contemplating — but he is not alone, as Tzemach Atlas has been performing moral introspection up above, in the women’s section. He descends to accost Chaikl.

“Are you studying Musar by yourself?” Tzemach asks.

Chaikl responds: “I came into the shul to look at the carvings. The man who carved the lions, eagles, deer and leopards is a great artist.”

I think the strong suggestion of the book is that Chaikl’s obsession with beauty (and metaphor, as he is the author and poet as a young man) is roughly equivalent to Karelitz’s obsession with Torah. Both are capable of providing a strong moral influence on the subject, something that Tzemach Atlas is unable to comprehend. The book tells us again and again that Tzemach not only doubts God; he also does not comprehend beauty, and (as a consequence) has no respect for humanity — in himself or in others. He is a moral failure *because *he is a religious and aesthetic failure.

All of these themes are made much more explicit in Grade’s remarkable short story, My War With Hersh Rasseyner. He writes there — and Hersh Rasseyner is an adherent of musar who sounds quite a bit like Tzemach Atlas:

Reb Hersh, you say that I have forsaken a fountain of living waters for a broken cistern. I must tell you that you’re wrong. I draw water from the same fountain as you, only with a different vessel.

Karelitz believes in simple faith and an obsession devotion to Torah study to guide one’s moral behavior. Grade in The Yeshiva basically agrees — but extends that basic moral perspective to devotion to the humanities, in general.

]]>Axiom 2: There exists an “empty story,” i.e. a story where nothing happens.

Axiom 3: Two stories are the same if and only if they contain the same events in the same order.

Axiom 4: If is a story and is a story, “ then ” is also a story.

Axiom 5: For every story , there exists a story that contains story . In this case we say that is a **telling **of .

Axiom 6: A story exists that contains the empty story, the story containing the empty story, the story containing that story, the one containing that, etc. forever. This is called the neverending story.

…

Since there is a story where nothing happens, there is also a story that is a telling of that empty story. As a result, the story where nothing happens and *then* someone tells a story about nothing happening is also a story. This can keep on going indefinitely, populating the entire universe of stories with retellings about nothing.

*Boiled the elements down into the axioms*

*Mistook a fax for remedial tediums*

*It seems Ezekiel speaks to some*

*My mind was hazy and numb*

*And left hand gripped a clump of palladium*

*Saw the beast with the wings and the talons*

*The simple answer but it felt out of balance*

*Bad news like a blue screen of death*

*Besides the point, but which hue seems best?*

*I’ll keep conducting these autistic symphonies*

*These sentences have sentenced me*

*Like I didn’t have the sense to sense the mere*

*The presence grows weird*

*Doesn’t make sense but I don’t fear, not a damn thing*

*I live like a man who’s already dead*

*Like I had a motorcycle but my name is Zed*

*(I’ll be missed), said another clumsy alchemist*

*Like he just learned predicate calculus*

*The existential quantifier, a backwards EX*

*My rap career is a cataloging of defects*

*Copy edited by Ryan Seacrest*

*Like he must be new to this*

*Milo doesn’t exude hubris, chuuch*

*Like he must be new to this*

*Milo doesn’t exude hubris*

So on Lebesgue’s theory of the integral in 1903:

“The axioms specify what the integral is intended to do. They do not start from an idea that the integral is about, say area, or any other primitive concept. It is necessary to show that there is a model of these axioms, but once that is done it is at least possible to prove properties of the integral directly from the axioms and without reference to any model of them. The axioms are sometimes said to define their object implicitly, or to create it. There is no reference to a primitive concept available via abstraction from the natural world.”

And on Kronecker and Riemann:

“Neither man suggested that objects cannot be studied via their representations, but both believed that one must be vigilant to ensure that one establishes properties of the objects themselves and not the properties of merely this or that representation, and to this end it was best to avoid explicit representations whenever possible.”

I didn’t know about the Hausdorff paradox, which feels a lot like Godel. Gray’s summary: “on any plausible definition of the measure of a set there must be non-measurable sets.”

Borel ended up critiquing the use of the axiom of choice to call the paradox into question, but this was another step (apparently) in pushing people to accept that definitions of area are inherently imperfect — pushing us further away from meaning and belief in the representations.

Another interesting point from Gray: you know that thing about the unreasonable effectiveness of math? That wouldn’t have made any sense in the 19th or 18th centuries because math was coextensive with science. Like, there’s nothing surprising at all about the connection between math and the world back then, because math was an attempt to describe the world.

I’m interesting to read more, but I’m feeling as if a question has been answered. Whether we call it modernism or not, this is the time in the history of math when the connection between mathematics and the empirical world was made problematic. If we’re looking for the origins of the idea that math is “useless,” it’s going to be in this movement in mathematics between 1880 and 1920.

]]>Plato’s Ghost looks like a good place to start.

Plato’s Ghostis the first book to examine the development of mathematics from 1880 to 1920 as a modernist transformation similar to those in art, literature, and music. Jeremy Gray traces the growth of mathematical modernism from its roots in problem solving and theory to its interactions with physics, philosophy, theology, psychology, and ideas about real and artificial languages. He shows how mathematics was popularized, and explains how mathematical modernism not only gave expression to the work of mathematicians and the professional image they sought to create for themselves, but how modernism also introduced deeper and ultimately unanswerable questions.

Building on Gray’s work is this presentation by Susumu Hayashi, which introduces (to me at least) the notion of “mathematical secularization.”

I also came across The Great Rift.

In their search for truth, contemporary religious believers and modern scientific investigators hold many values in common. But in their approaches, they express two fundamentally different conceptions of how to understand and represent the world.

Michael E. Hobartlooks for the origin of this difference in the work of Renaissance thinkers who invented a revolutionary mathematical system—relational numeracy. By creating meaning through numbers and abstract symbols rather than words, relational numeracy allowed inquisitive minds to vault beyond the constraints of language and explore the natural world with a fresh interpretive vision.

The focus is on early modernity and the shift to algebra, which is an earlier phenomenon than modernism. But maybe it’s part of the same story?

Also in the category of “is this related? maybe??,” there is a working group of philosophers that call themselves the Mathematics, Mysticism and Secularization working group.

There are all these -isms that I learned about in philosophy of math: empiricism, logicism, formalism, fictionalism (wiki). That’s part of this story too.

What I’m attracted to is the idea that math is as much a part of culture as anything else. Over the last few centuries Western society has gotten less and less comfortable with the abstract, invisible realm of religion and spirits. Wouldn’t that have an impact on how that culture thinks about that other invisible, abstract realm of mathematics?

People used to think of as referring just to a square’s area, but then it was emptied of that meaning. Is the break of algebra from geometry something like the break of philosophy from theology?

People used to think that mathematics was a search for ultimate truths, not just conditional ones. Are we living in a mathematically relativistic world?

Mathematicians sometimes talk — with pride! — of the uselessness of their work. Is that the end result of the sorts of processes described by these authors?

I have no clue, and I have no idea when I’ll be able to read those books. But the questions seem interesting and confusing.

]]>Better versions of this are readily available in practically any textbook, but Illustrative Math has a totally free and online unit on exponents that does this activity better. It’s less tedious and repetitive and it asks questions to push students towards generalizations, rather than asking kids to churn out rows and notice the structure at the very end (“discovery”).

Yes, it’s at a Grade 8 level, but this lesson is pretty much there too. And if you can wait a few months, you’ll have the high school version available too.

]]>**But a lot of your most danceable songs have very profound lyrics.**

*I don’t know, this thing about lyrics – I’m just catching on to this. If you get some of the facts together . . . I mean, I sell records in places where they don’t speak English. And I’ve experienced listening to Greek singers, for instance, and not knowing what the words are, but I get a story and a feeling from it even though I haven’t a clue to what’s being said. So if English-language songs can sell in non-English-speaking countries and people can be touched by them, then we can see how irrelevant the words are.*

**Sometimes it seems that you let the words dance when you sing them; you release them, and they take off in their own directions.**

*The only time I actually work with words is when I’m writing a song. After it’s written, I release the words; and every time I’m singing, I’m singing syllables. I’m just singing signs and phrases.*

But this can’t be the whole story. Music with incomprehensible lyrics isn’t the same as listening to instrumental music. It’s also not the same as listening to scat or wordless yammering. Somehow the presence of words — maybe it’s just the possibility of meaning — changes the way we listen to a song.

]]>A #precalc student is wondering about continuous induction – is this a thing? If so, how does it work? How do we define a 'next' step for a continuous set of numbers? How do you prove things about this 'next,' if so? Can proof by induction get done in this way? #MTBoS #iTeachmath

— Anna Blinstein (@ablinstein) January 23, 2019

Great answer: Yes!

Is there a version of mathematical induction that can be used to prove facts about the *real* numbers? Yes there is! See Pete Clark’s “The Instuctor’s Guide to Real Induction”. https://t.co/gchuXFbdwb

— James Propp (@JimPropp) January 27, 2019

From the paper:

Consider “conventional” mathematical induction. To use it, one thinks in terms of

predicates —i.e., statements indexed by the natural numbers — but the cleanest statement is in terms ofsubsetsof The same goes for real induction.

I think of induction as being about dominoes falling, but the focus on sets is a different way of talking about induction — even for the natural numbers.

To be OK with this paper’s explanation of continuous induction, we have to be OK with the idea that its sets that the inductive property — it’s not a process metaphor, it’s a property metaphor, or something like that. Maybe a useful metaphor is flammability, rather than dominoes. Some sets are made of stone. Others you set a spark and the whole thing goes up in flames. Those are the inductive sets.

Here’s what it means for a set of real numbers to be inductive:

The three conditions say what it means to be inductive, and the theorem states that if a set is inductive then it is fire: something that’s true for part of that inductive set has to be true for the whole thing.

(Something I’m wondering about real induction: can’t the spark can be planted either at the front or back of the set? I think with slightly different conditions for inductivity you could start this at b.)

The paper goes on to use this continuous induction to prove some of the classic theorems of calculus and analysis, including the Intermediate Value Theorem. Here’s my attempt to restate the proof in the paper.

So, I’m going to tell you three things about a graph. First, it starts like this and ends at 10:

Second, the function is continuous.

Third, the function **does not ever cross zero.**

Question: Are you guaranteed that this graph stays positive the whole time?

Answer: Yes, duh. But as with a lot of this foundational stuff, the challenge is to say why.

So let’s make the following inductive argument, by first collecting all the inputs 0 through 10 of my function that yield positive outputs into a set. So far, just from the graph, you know that this set contains all the real numbers from 0 to about 2. We’d love to show that actually all the real numbers from 0 through 10 are part of this set.

Now, let’s tee up the conditions for this set being inductive.

- 0 is in this set, because duh I showed you that 0 is in this set.
- Pick any number that’s already in this set — it looks like 2.2 is in it — then there
*has*to be some larger number in the set i.e. also yields a positive output. That’s because this function is continuous, and so approaching 2.2 from the right, eventually the outputs need to get really, really, REALLY close to the true output when 2.2 is the input to*f*. That necessarily means that it’s going to have a positive output, since the output of 2.2 is positive. So there needs to be numbers larger than 2.2 that are in this set if the function is continuous. - And suppose that you knew some range from 0 up to
*but not necessarily including*8 where*f*was positive, i.e. still hanging out above that zero line. Well, even though we “but not necessarily including”-ed 8, 8 has got to be positive anyway. Because go backwards*at all*from 8 and you should hit positive outputs, but because this*f*is continuous eventually all those positive values need to be (eventually) super-duper-duper close to . So 8 must have a positive output.

And by induction, tada, there’s nothing stopping you from extending this to the entire domain of 0 to 10, it’s positive the whole way through. And since this is just a restatement of the Intermediate Value Theorem, you’ve proven that too, by induction.

I still have questions, but this is very cool.

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