An inexpensive hardback of Introducing Category Theory was published on June 1st, and is beginning to appear listed on booksellers’ online sites — search with the ISBN 106834671X. #mathsky #philsky

I'm migrating Logic Matters from an expensively hosted Wordpress incarnation to a freely hosted GitHub site. Wish me luck! Here's a first version -- all comments most welcome. logicmatters.github.io/logic-matter... #philsky #mathsky

The revised/corrected third edition of *Introducing Category Theory* is now available as a paperback. To keep the cost down it is Amazon-only print-on-demand with ISBN 1068346728. Sorry! -- but the PDF remains freely downloadable from logicmatters.net for Amazon refuseniks ...

I never knew what was so great about the "great icosahedron". Now I do! Take a regular icosahedron whose vertices have coordinates in ℚ[√5]. Apply the nontrivial element of the Galois group: that is, replace √5 by -√5. You get the great icosahedron! (1/n)

There have been so many moving obituaries and fond tributes. Here, to mark her passing, is Felicity Lott at the start of her stellar career, singing Pamina at Glyndebourne, almost fifty years ago. How joyous.

A (not very exciting but possible useful) blog post on my experiences using LLMs as proofreading assistants. Headline news: they are very useful but also very surprisingly unreliable. www.logicmatters.net/2026/05/17/p... #mathsky #philsky

There's a newly revised version of my *Introducing Category Theory* notes -- correcting an embarrassing number of typos and a few thinkos in the previous version. A pbk follows, but meanwhile here's a link to the (free!) PDF: www.logicmatters.net/resources/pd... #Mathsky #Philsky

Elizabeth Brauß gave a really wonderful performance of Schubert’s first set of Impromptus at a concert a few years ago. The BBC have broadcast it again. Listen -- it will make your day better! www.bbc.co.uk/sounds/play/... (starting at 5.12.40 in) #Schubert #Piano

It almost seems a shame to hide the new wallpaper with books ... but needs must! #booksky

A quick blog post commenting on the claim by Alex Oliver and Tim Smiley to have shown that the “easy” direction of Church's Thesis is wrong. I'm not persuaded -- and neither should you be! www.logicmatters.net/2026/04/06/p... #philsky #mathsky

One of my favorite works by Schubert -- his Impromptu No. 3 in G-flat major -- played superbly by German pianist Elisabeth Brauß and posted by German public broadcasting. www.youtube.com/watch?v=4tWc...

Elisabeth Brauss played Mozart's 23rd Piano Concerto at the Cartagena Festival de Música ten days ago.A terrific performance she evidently much enjoyed. www.youtube.com/watch?v=rX5c...

There's a new version of my *Introducing Category Theory* now available -- a freely downloadable PDF and also a very-cheap-for-its-size pbk. Enough corrections/improvements to count as a "third edition". For info/link see logicmatters.net/categories Please spread the word! #MathSky #PhilSky

The second issue of the new Journal for the Philosophy of Mathematics is now online (open access). Includes five pieces on sets and pluralities which (on a quick browse) seem interesting and good. Take a look! #MathSky #PhilSky riviste.fupress.net/index.php/jpm

Today’s epiphany… here the adoration of the magi by Fra Angelico & Fra Filippo Lippi 1440-60. National gallery of art Washington DC.

A new blog post about using AI in proofreading the upcoming revised 2nd edition of my category theory book. Might be of interest to other maths writers. www.logicmatters.net/2025/12/28/a... #MathSky

There will be a revised version of my category theory book in January. Mostly minor changes for reader-friendliness. But I have expanded the short chapter on ETCS at the very end of the book into two short chapters. Here's a draft: www.logicmatters.net/resources/pd... Comments very welcome! #MathSky

Wonderful concert by Elisabeth Brauss at Wigmore Hall on Tuesday. Her Beethoven Op. 110 particularly moving -- www.youtube.com/watch?v=Puyd...

Paul Klee The Bounds of the Intellect, 1927

Daily Nous has a nice list of currently active philosophy blogs at dailynous.com/2025/09/18/t... It doesn't mention Logic Matters, but it staggers on into its twentieth year, still with occasional logic and phil maths content, at www.logicmatters.net/blog

New double CD of Lea Desandre and Thomas Dunford (and the Jupiter Ensemble) performing Dowland and Purcell. Absolutely superb playing and often extraordinarily moving. (Had the good fortune to see them live at Wigmore Hall last week -- just stunning.)

CD Forthcoming soon! Love the cover photo :)

First 5 star Amazon rating AND first typo report for new edition of *Introducing Category Theory*. Ah well ...

New blog post ... on Van Gogh, Deryn Rees-Jones (@notjustdancing.bsky.social), Proust, Clive James: www.logicmatters.net/2025/07/12/p...

I've updated my page of links to entry-level lecture notes and online books on category theory. The page is visited a lot (3K times a month) so I ought to try to keep it in good shape. So any additions/corrections will be really welcome! www.logicmatters.net/categories/ #mathsky #philsky

ICYMI At last, there is a pbk version of my notes *Introducing Category Theory*, 2nd edn., ISBN 1068346701. Amazon-only print on demand to keep the price minimal for a 500pp book. Or you can still download the PDF from logicmatters.net. Spread the word :) #mathsky #philsky

Sound the trumpets ... At last, at last, there is a pbk version of my notes *Introducing Category Theory*, 2nd edn., ISBN 1068346701. Amazon-only print on demand to keep the price minimal for a 500pp book. Or you can still download the PDF from logicmatters.net. Spread the word :)

The linked piece by Keith Frankish on what LLMs are doing is (characteristically) excellent.

Simply wonderful Schubert playing from Elisabeth Brauß www.bbc.co.uk/sounds/play/... From about 18 mins into the programme (available for about a month).

You can now download a complete version of *Introducing Category Theory* from www.logicmatters.net/categories. Just needs final proofreading. Has it any virtues? Well, at least it might distract you for a while, as the world goes to hell in a handcart ... #mathsky #philsky

‘The Easter bunny was a hare long before he was a rabbit; the hare was sacred to Eostre, the Saxon goddess of spring – no rabidly cute bundle of fluff.’ Katherine Rundell considers the hare: www.lrb.co.uk/the-paper/v4...

Elisabeth Brauß playing the last movement of Beethoven's 4th Piano Concerto. Joyous! www.youtube.com/watch?v=OJX0...

Here are links to a dozen blog posts "Schubert on Sunday", linking mostly to some wonderfully good YouTube videos. You might well have missed some -- take a quick look! #Schubert www.logicmatters.net/tag/schubert...

There's a terrific new Schubert CD by Charlotte Saluste-Bridoux and her piano duo partner Joseph Havlat. www.delphianrecords.com/products/sch... Here's a link to their playing the Fantasia D. 934 at Wigmore Hall (and some other Schubert links too). Enjoy! www.logicmatters.net/tag/schubert...

@classicalmusic Wolfgang Amadeus Mozart - 12 Variationen über "Ah, vous dirai-je Maman" für Klavier C-Dur, KV 265 Elisabeth Brauß, Klavier https://www.youtube.com/watch?v=3d7L14O9BOY #Music #classic #piano

Schubert on Sunday. A quite terrific performance of the Trout Quintet. www.gstaaddigitalfestival.ch/en/video/pat... (You may have to sign up to the Gstaad site, but that's free.)

I lied. I said "apart from proof reading for typos and thinkos, this [posted yesterday] is the version which will be paperbacked". But today there's a new version of *Introducing Category Theory* with improved last chapter. And so it goes. www.logicmatters.net/categories/ #mathsky #philsky

There's a new complete version of *Introducing Category Theory* downloadable at logicmatters.net/categories Apart from proof reading for typos and thinkos, this is the version which will be paperbacked (as cheaply as possible) in May. So let me know of any errors, however small! #mathsky #philsky

My good friend, the logician Thomas Forster, tells me that he once shared an office with Giovanna Corsi, who at one point shared an office with Jean van Heijenoort, who was Trotsky's personal secretary in the 1930s ....  Just four handshakes from Trotsky.

Belatedly (real life happens ...), there's a complete version of my *Introducing Category Theory*. A month's tinkering now, and there should be a cheap pbk. But you can download a draft for free from www.logicmatters.net/categories #mathsky #philsky

Elisabeth Brauss concert a week ago … Bach, Beethoven, Hough, Schumann, Prokofiev. Wonderful performances very engagingly filmed. m.youtube.com/watch?v=4gqb...

The terrific Elisabeth Brauß enjoying herself playing Mozart. www.ardmediathek.de/video/ard-kl...

Great tits have started today zipping in and out of the bird box on the garage, carrying nesting material … … these days we take the little moments of hope when we can!

“As the clever hopes expire, Of a low dishonest decade… The enlightenment driven away, The habit-forming pain, Mismanagement and grief: We must suffer them all again…” September 1 1939, by W.H. Auden, English poet, born #OTD 1907. Portrait by Cecil Beaton 1930, National Portrait Gallery London

Cutting-edge category theory research question. Suppose you use "NNO" to abbreviate "natural numbers object". Do you then write "a NNO" or "an NNO"? Hmmmmmmm. Tough one? (Hope your morning is going as productively ....) #mathsky #philsky

Apple Watch: Take a moment to reflect… Pause: Me: Hell’s bloody bells …

Lots of bad things happening but at least it’s #SuperbOwl Sunday

The performance of La Traviata, with Lisette Oropesa as Violetta, broadcast from the Royal Opera House last night was wonderful with Oropesa just stunning. You can catch it on the BBC for a month. Don’t miss the chance. www.bbc.co.uk/programmes/m...

Update: You might want the latest version (now 2.5) of *Introducing Category Theory* (a mere 462 merry pages). Or you might very sensibly much prefer links to Elisabeth Brauß and Maria Joāo Pires playing Mozart. Either way, you might like www.logicmatters.net/2025/02/03/i... #mathsky #philsky