| While there are certainly incentive problems and simple cruft in that regard[1]... Generally, writing textbooks is just hard and nobody really knows how to do it. Textbooks as they are usually understood[2] are, above all, books[3], that is, large flowing pieces of prose that tell a story about an area of knowledge in a generally linear manner. This is not how knowledge works. At least the way I feel my knowledge is organized when I try to explain things is that I have a sprawling weighted (on a scale from “vague association” to “hard prerequisite”) graph with rather compact ideas as vertices of absolutely enormous degree (at least in regions I feel I have a decent understanding of). Only by several iterations of merciless pruning around the desired generating set can I get a subgraph that is concise enough that I have some hope of explaining it in the available time, parsimonious enough that I can toposort it onto the time axis without people’s heads spinning and stacks overflowing, and comprehensive enough that I don’t feel I’ve given people a horribly skewed impression and don’t risk choosing a perspective so narrow that would fail to engage some of them. Then comes the actual work of (choosing a) linearization, which I can kind of do in my head for stories of no more than a couple hours at the cost of something like 15 minutes of confusion-inducing backtracking per hour, but it gets exponentially harder as you go past these limits, and you have to go pretty far past them to reach good writing. All of these decisions are kind of like those in an optimizing compiler in that they really want to feed into each other, but actually letting them do so would cause the process to come to a grinding halt, so you interate and order and apply vague heuristics and make arbitrary choices and your inner perfectionist hates you the whole time you’re doing it. And you get to do this practically from scratch every single time because the given context and the desired focus are virtually never the same. You might say at this point that this is what I get for choosing a wire representation (books and more generally stories) so unlike the in-memory representation (graphs of associations). That may be true to some extent[4], but it’s also important to realize that what is best for knowledge storage doesn’t have to be any good for knowledge acquisition[5]. In fact, the omission that bothers me most of the ones I made in the book-writing rant above is that I know of some things that are just so cute and smol sitting in my head, but when I try to get them out I either assume so many prerequisites that there’s nothing to get out or end up staring at a plan for what is at best a terse twenty-page essay I’m never going to write. I wish hard for viable alternatives to linear narrative, but I also realize I haven’t encountered any that were nearly as good or universally applicable. You can certainly point people at a pile of short-form hypertext, but that misses the issue of pruning: doing it effectively requires you to already know things you decide to prune and the general layout of the subject on a level that is, in classroom terms, several years beyond what you are trying to isolate; a learner is incapable of doing this or at the very least is going to waste tremendous amounts of time doing a mediocre job of it. (I certainly did when I was learning maths from Wikipedia.) I don’t mean to denigrate anyone’s intellectual capability here, or even dissuade them from literature surfing. Surfing in moderation is useful and efficient. I’m only saying that the apparently obvious solution of switching out books for a hyperlinked card catalogue fails and fails hard. Teaching and books are hard and nobody really knows the secret to doing them well, even those who are brilliant at them. There are a lot of arbitrary choices (not really, but heavily reader-dependent, including factors unknowable to the writer or even the reader) involved in making a book. We solve that problem by throwing a lot of them at the audience and seeing what sticks to whom. But that means a perfect book is impossible—not “drink the ocean” impossible, but “draw a round square” impossible[6]. The problem doesn’t even make sense; what’s a perfect book to you can be a hideous book to me, and what’s a perfect book for me right now was an impenetrable book for me ten years ago. There are objectively good books and objectively bad books, but objectively perfect is something a book cannot be. [1]: Nobody is going to count your Wikibooks contributions towards your tenure; also, Wikibooks and MediaWiki in general managed to find that sweet spot where they’re simultaneously so expressive you can’t reliably process them automatically and so limited they don’t make good self-contained books, neither fixed nor reflowable. [2]: Let’s say pre-1970—I find modern trends in English-language secondary and basic undergrad texts positively cringeworthy, but I haven’t ever had to use them in either capacity. [3]: Can’t help but be reminded here of Michele Audin’s deliciously snarky Tautology 2.3.1 from “Conseils aux auteurs des textes mathématiques”, <http://irma.math.unistra.fr/~maudin/newhowto.ps>. [4]: The only tool or process I’ve found which is even remotely adapted to this data model is TiddlyWiki <https://tiddlywiki.com/>, which I tried, but never could get over its many quirks and primitive organizational features to make it useful even for notes to myself, let alone as an interface with others. [5]: For example, fluent readers of Latin/Greek/Cyrillic-script languages generally work by recognizing shapes of words on a page, often for several words in parallel, but teaching children or non-Latin/Greek/Cyrillic-literate adults to read this way is a famously useless affair. [6]: This also means mandatory texts for students and even mandated curricula for teachers are an atrocity which sacrifices a whole lot of adaptation capability for a modest bit of ease in detecting incompetence and bad faith. The more often a curriculum is nailed down to the time axis with tests and metrics the worse it is. |
> [T]here are many books that violate the principle of having something to say by trying to say too many things. Teachers of elementary mathematics in the U.S.A. frequently complain that all calculus books are bad. That is a case in point. Calculus books are bad because there is no such subject as calculus; it is not a subject because it is many subjects. What we call calculus nowadays in the union of a dab of logic and set theory, some axiomatic theory of complete ordered fields, analytic geometry and topology, the latter in both the “general” sense (limits and continuous functions) and the algebraic sense (orientation), real-variable theory properly so called (differentiation), the combinatoric symbol manipulation called formal integration, the first steps of low-dimensional measure theory, some differential geometry, the first steps of the classical analysis of the trigonometric, exponential, and logarithmic functions, and, depending on the space available and the personal inclinations of the author, some cook-book differential equations, elementary mechanics, and a small assortment of applied mathematics. Any one of these is hard to write a good book on; the mixture is impossible.
... But I should probably explain the general picture somewhat for the reader who’s unable to follow the deluge of terminology here.
The problem with calculus, in terms of my parent comment, is that it hasn’t been a singular cluster or clique of ideas in any working mathematician’s association graph since the time of Euler; the list of topics that is presented under that name has never been such—it’s both anachronistically rich in trying to include insights from Weierstrass’s rigour to Tychonoff’s point-set topology and anachronistically poor in avoiding Newton’s motivation from algebraic geometry and differential equations or Euler’s motivation from complex analysis and homotopy theory.
So, if we don’t have a justification from either history or state of the art, why do we insist on this low-resolution camrip of Newton and Leibniz’s writings sprinkled with an arbitrary selection of later work? I don’t know, but I suspect that this is simply the best people could fit into the allotted time when they last tried to incorporate actual, live mathematics into the general curriculum at the beginning of the 20th century, after a hundred years of vulgarization erosion and haphazard contradictory pushes for modernization and practicality.
Why should you even care how mathematicians think now or thought in the past? You don’t have to, of course, though in that case I would much prefer that you avoid diluting the brand “mathematics” by attaching it to the result[2]. But a course should be about something; either you’re teaching mathematics as a matter of culture and way of thought (you sure as hell don’t have time to teach it as a field of study), or you’re reaching for a particular application (but you better know which one, because an applied course left adrift soon becomes a patchwork zombie).
Either way those funny mathematicians in their ivory towers can be of use for you, because they haven’t simply spent all these years playing with impractical abstractions: they broke every subject including old-school calculus into patterns, distilled those patterns into their most elementary possible forms in the form of impractical abstractions, then went back and rearranged their understanding of each subject to make the forms they found more evident, then did it again and again. For decades.
Unfortunately for us lovers of simple answers, their conclusion was, “calculus is not a single thing”. Is there a course or two struggling to come out in the general vicinity so labelled? Yes, but while I have some speculations as to what they are, I don’t have a actual plan—that takes years of regular experimentation with and on classes of real students. It probably includes more varied topics compared to the current approach, certainly some formal series and a glimpse beyond dimension one, probably even a bit of linear algebra as a geometric foundation for it all. (Also a pony while we’re at it.) Should we teach them when combinatorics is infinitely more accessible and probability theory is infinitely more practical? I think so, if not for the cultural significance and life wisdom[3], then because any physics worth speaking of is practically inexpressible without it.
Sorry, I don’t have an answer for you; if I had, it would’ve already been one of those many, many books.
(Took me until the middle of the second of my two answers to realize they both essentially say “Your question is ill-posed” from different points of view; hope they are a bit more helpful than just that.)
[1]: https://www.mathematik.uni-marburg.de/~agricola/material/hal...
[2]: https://www.maa.org/external_archive/devlin/devlin_03_08.htm...
[3]: <https://www.basicbooks.com/titles/jason-wilkes/burn-math-cla...>, <https://www.blackdogandleventhal.com/titles/ben-orlin/change...>