The Joy of Abstraction

The Topos Institute is starting book club for The Joy of Abstraction by Eugenia Cheng. This book is an introduction to category theory for anyone who wants to get into the formality of the subject but does not necessarily have the mathematical background to read a standard textbook. Part 1 starts gently, so that readers can build up to the formality of rigorous mathematics even if they haven’t encountered it before. Part 2 gets into category theory, including limits and colimits, duality, functors, natural transformations, and the Yoneda lemma.

For more information about the book, try this:

Dr. Cheng would like to give people an opportunity to ask questions and get help with understanding the book. The book club will be hosted by the Topos Institute and will be run asynchronously. They will go at an approximate rate of one chapter per week. You can submit questions for each chapter according to the published schedule. Questions for the first chapter are due February 19, 2023. They will collate the questions and Dr. Cheng will make a video each week addressing the questions for that chapter. You will remain anonymous when asking the questions, so please don’t hesitate to ask questions that might feel “stupid”. They welcome any question that comes from you wanting to understand something better!

Each video will be posted at

during the week following the deadline for questions. If you are ahead of schedule you are welcome to submit questions in advance, but they will only be addressed in the video for that chapter.

To submit questions, please fill in this Google form. Include a page reference for your question, if relevant, so that Dr. Cheng can address the questions in order in the video.

This book club is open to everyone everywhere. Please spread the word!

Note that the schedule may change, but the deadlines for each chapter will only become later, never earlier.

5 Responses to The Joy of Abstraction

  1. Among other things, below are some of the books I will be reading and studying this semester:

    A critique of “stakeholder capitalism”: The Profit Motive by Steven Bainbridge (more details here, via Volokh);
    An introduction to category theory, the cover of which is pictured below: The Joy of Abstraction by Eugenia Cheng (more details here, via Azimuth);
    A “short history of what we live by”, which was recommended to me by Stephen Carter: Rules by Lorraine Daston (more details here, via Next Big Idea Club);
    A collection of essays about Adam Smith: Smithian Morals by Dan Klein (an open access version is available here);
    A history of mid-19th century accounting and finance clerks: Accounting for Capitalism: The World the Clerk Made by Michael Zakim (more details here, via the London School of Economics).

  2. Manuel says:

    I am going to be joining this – just finished the prologue, will be starting chapter 1 in a minute.
    It is a pity you are no longer on twitter, Mr. Baez.

  3. Mark Weitzman says:

    Ok took the bait and started reading the book. Not sure if I have the target background for the book – I have an undergraduate degree in mathematics, and a Masters degree in theoretical physics. Also my favorite mathematics books are by authors like the late H.M. Edwards (e.g. Fermat’s Last Theorem – A Genetic Introduction to Algebraic Number Theory) where concrete examples and calculations are used to build up the formalism, rather than Bourbaki style of mathematics.

    • John Baez says:

      Since you have an undergrad degree in math, you may find the beginning chapters of Cheng’s book easy (though even those are full of insights). But by the time you get to limits and colimits, adjoint functors and the Yoneda Lemma, you’ll probably be learning some new math—and some very beautiful math, as well.

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