PhD, Postdoc with Rosalie Iemhoff

Postdoc position in Logic at Utrecht University, the Netherlands. The postdoc is embedded in the research project “Optimal Proofs” funded by the Netherlands Organization for Scientific Research led by Dr. Rosalie Iemhoff, Department of Philosophy and Religious Studies, Utrecht University. The project in mathematical and philosophical logic is concerned with formalization in general and proof … Continue reading PhD, Postdoc with Rosalie Iemhoff

Raymond Smullyan

Proof by legerdemain

Peli Grietzer shared a blog post by David Auerbach on Twitter yesterday containing the following lovely quote about Smullyan and Carnap: I particularly delighted in playing tricks on the philosopher Rudolf Carnap; he was the perfect audience! (Most scientists and mathematicians are; they are so honest themselves 'that they have great difficulty in seeing through … Continue reading Proof by legerdemain

Rumfitt on truth-grounds, negation, and vagueness

Zach, Richard. 2018. “Rumfitt on Truth-Grounds, Negation, and Vagueness.” Philosophical Studies 175 (8): 2079–89. https://doi.org/10.1007/s11098-018-1114-7. In The Boundary Stones of Thought (2015), Rumfitt defends classical logic against challenges from intuitionistic mathematics and vagueness, using a semantics of pre-topologies on possibilities, and a topological semantics on predicates, respectively. These semantics are suggestive but the characterizations of … Continue reading Rumfitt on truth-grounds, negation, and vagueness

Why φ?

Yesterday, @gravbeast asked on Twitter, Does anyone know why we traditionally use Greek phi and psi for metasyntactic variables representing arbitrary logic formulas? Is it just because 'formula' begins with an 'f' sound? And chi was being used for other things? Although Whitehead and Russell already used φ and ψ for propositional functions, the convention … Continue reading Why φ?

Logic Colloquium, Udine

The European Summer Meeting of the Association of Symbolic Logic will be in Udine, just north of Venice, July 23-28. Abstracts for contributed talks are due on April 27. Student members of the ASL are eligible for travel grants! lc18.uniud.it  

Ptolemaic Astronomy

Working on the chapters on counterfactual conditionals for the Open Logic Project, I needed some illustrations for David Lewis's sphere models, which he jokingly called "Ptolemaic astronomy." Since Franz Berto joked that this should just require \usepackage{ptolemaicastronomy}, I wrote some LaTeX macros to make this easier using TikZ. You can download ptolemaicastronomy.sty (it should work … Continue reading Ptolemaic Astronomy

Modal Logic! Propositional Logic! Tableaux!

Lots of new stuff in the Open Logic repository! I’m teaching modal logic this term, and my ambitious goal is to have, by the end of term or soon thereafter, another nicely organized and typeset open textbook on modal logic. The working title is Boxes and Diamonds, and you can check out what’s there so far on the builds site. This project of course required new material on modal logic.  So far this consists in revised and expanded notes by our dear late colleague Aldo Antonelli. These now live in content/normal-modal-logic and cover relational models for normal modal logics, frame correspondence, derivations, canonical models, and filtrations. So that’s one big exciting addition. Since the OLP didn’t cover propositional logic separately, I just now added that part as well so I can include it as review chapters. There’s a short chapter on truth-value semantics in propositional-logic/syntax-and-semantics. However, all the proof systems and completeness for them are covered as well. I didn’t write anything new for those, but rather made the respective sections for first-order logic flexible. OLP now has an FOL “tag”: if FOL is set to true, and you compile the chapter on the sequent calculus, say, you get the full first-order version with soundness proved relative to first-order structures. If FOL is set to false, the rules for the quantifiers and identity are omitted, and soundness is proved relative to propositional valuations. The same goes for the completeness theorem: with FOL set to false, it leaves out the Henkin construction and constructs a valuation from a complete consistent set rather than a term model from a saturated complete consistent set. This works fine if you need only one or the other; if you want both, you’ll currently get a lot of repetition. I hope to add code so that you can first compile without FOL then with, and the second pass will refer to the text produced by the first pass rather than do everything from scratch. You can compare the two versions in the complete PDF. Proofs systems for modal logics are tricky; and many systems don’t have nice, say, natural deduction systems. The tableau method, however, works very nicely and uniformly. The OLP didn’t have a chapter on tableaux, so this motivated me to add that as well. Tableaux are also often covered in intro logic courses (often called “truth trees”), so having them as a proof system included has the added advantage of tying in better with introductory logic material. I opted for prefixed tableaux (true and false are explicitly labelled, rather than implicit in negated and unnegated formulas), since that lends itself more easily to a comparison with the sequent calculus, but also because it extends directly to many-valued logics. The material on tableaux lives in first-order-logic/tableaux. Thanks to Clea Rees for the the prooftrees package, which made it much easier to typeset the tableaux, and to Alex Kocurek for his tips on doing modal diagrams in Tikz.

Making an Accessible Open Logic Textbook (for Dyslexics)

In the design and layout of the Open Logic Project texts as well as the Calgary Remix of the intro text forall x, we’ve tried to follow the recommendations of the BC Open Textbook Accessibility Toolkit already. Content is organized into sections, important concepts are highlighted (e.g., colored boxes around definitions and theorems), chapters have summaries, etc. We picked an easily readable typeface and set line and page lengths to enhance readability according to best (text)book design practices and research. We’ve started experimenting specifically with a version of forall x that is better for dyslexic readers (see issue 22). Readability for dyslexics is affected by typeface, type size, letter and line spacing. Charles Bigelow gives a good overview of the literature here. Some typefaces are better for dyslexic readers than others. Generally, sans-serif fonts are preferable, but individual letter design is also relevant. The British Dyslexia Association has a page on it: the design of letters should make it easy to distinguish letters, not just when they are close in shape (e.g., numeral 1, uppercase I and lowercase l; numeral 0, uppercase O and lowercase o, lowercase a) but also when they are upside-down or mirror images (e.g., p and q, b and d; M and W). In one study of reading times and reported preference, sans-serif fonts Arial, Helvetica, and Verdana ranked better than other fonts such as Myriad, Courier, Times, and Garamond, and even the specially designed Open Dyslexic typeface. Although it would be possible to get LaTeX to output in any available typefaces, it’s perhaps easiest to stick to those that come in the standard LaTeX distributions. The typeface that strikes me as best from the readability perspective seems to me to be Go Sans. It was designed by Bigelow & Holmes with readability in mind and does distinguish nicely between p and q; b and d; I, l, and 1, etc. Other things that improve readability:
  • larger type size
  • shorter lines
  • increased line spacing
  • increased character spacing, i.e., “tracking” (although see Bigelow’s post for conflicting evidence)
  • avoid ALL CAPS and italics
  • avoid word hyphenation and right justified margins
  • avoid centered text
The accessible version of forall x does all these things: Type size is set to 12 pt (not optimal on paper, but since this PDF would mainly be read on a screen, it looks large enough). Lines are shorter (about 40 instead of 65 characters per line). Line spacing is set at 1.4 line heights. Tracking is increased slightly, and ligatures (ff, fi, ffi) are disabled. Emphasis and defined terms are set in boldface instead of italics and small caps. Lines are set flush left/ragged right and words not hyphenated. The centered part headings are now also set flush left. The changes did break some of the page layout, especially in the quick reference, which still has to be fixed. There is also some content review to do. In “Mhy Bib I Fail Logic? Dyslexia in the Teaching of Logic,” Xóchitl Martínez Nava suggests avoiding symbols that are easily confused (i.e., don’t use ∧ and ∨), avoid formulas that mix letters and symbols that are easily confused (e.g., A and ∀, E and ∃), and avoid letters in the same example that are easily confused (p, q). She also recommends to introduce Polish notation in addition to infix notation, which would not be a bad idea anyway. Polish notation, I’m told, would also be much better for blind students who rely on screen readers or Braille displays. (The entire article is worth reading; h/t to Shen-yi Liao.) Feedback and comments welcome, especially if you’re dyslexic! There’s a lot more to be done, of course, especially to make the PDFs accessible to the vision-impaired. LaTeX and PDF are very good at producing visually nice output, but not good at producing output that is suitable for screen readers, for instance. OLP issue 82 is there to remind me to get OLP output that verifies as PDF/A compliant, which means in particular that the output PDF will have ASCII alternatives to all formulas, so that a screen reader can read them aloud. Even better would be a good way to convert the whole thing to HTML/MathML (forall x issue 23). forallxyyc-accessible

Logic Courseware?

Kit Fine asked me for suggestions of online logic materials that have some interactive component, i.e., ways for students to build truth-tables, evaluate arguments, translate sentences, build models, and do derivations; ideally it would not just provide feedback to the student but also grade problems and tests. There is of course Barwise & Etchemendy's Language, … Continue reading Logic Courseware?

Citations in your CV

I drank the Koolaid and set up my CV so it's generated automatically from a YAML file with a Pandoc template. The basic functionality is copied from bmschmidt/CV-pandoc-healy. My version generates the bibliography from a BibTeX file however, using biblatex.  The biblatex code is tweaked to include links to PhilPapers and Google Scholar citation counts. … Continue reading Citations in your CV

Illuminated Manuscript of Aristotle, Averroes, and Ramon Llull Charging the Tower of Falsehood

Jonathan Greig (LMU Munich) posted the picture above to Twitter the other day, crediting Laura Castelli with finding it. It's from a 14th Century illuminated manuscript by Thomas Le Myésier, Breviculum ex artibus Raimundi Lulli electum, and depicts Aristotle, Averroes, and Ramon Llull leading an army charging the Tower of Falsehood. I put a full … Continue reading Illuminated Manuscript of Aristotle, Averroes, and Ramon Llull Charging the Tower of Falsehood

New in Print: forall x (Summer 2017 edition), and Incompleteness and Computability

New on Amazon: the print version of the Summer 2017 edition of forall x: Calgary Remix, as well as the text I made for Phil 479 (Logic III) last term, Incompleteness and Computability. The new edition of forall x includes a number of corrections submitted by Richard Lawrence, who taught from it at Berkeley in the Spring term. I’ve also noticed that if you don’t want Amazon to distribute the book to libraries and bookstores, you can make it a lot cheaper: USD 7.62 instead of USD 11.35.  Of course, the PDF is still free. (There’s now also a version for printing on letter-sized paper.) With Richard’s and Aaron’s help, the solutions manual now matches the text and has fewer errors.

Links to Amazon: US UK Canada Germany

The print version of Incompleteness and Computability incorporates a number of corrections and improvements suggested by my Logic III students. Compared to the version announced earlier, it also includes the two new chapters on Models of Arithmetic and on Second-order Logic. It, too, is still available free in both PDF and source code.

Links to Amazon: US UK Canada Germany

Aldo Antonelli’s last paper

Aldo Antonelli's last paper, "Completeness and Decidability of General First-Order Logic (with a Detour Through the Guarded Fragment)" is now out in the most recent issue of the Journal of Philosophical Logic. This paper investigates the “general” semantics for first-order logic introduced to Antonelli (Review of Symbolic Logic 6(4), 637–58, 2013): a sound and complete … Continue reading Aldo Antonelli’s last paper