What does demonology have to do with logic?

I recently found out (through falling into a research rabbit hole courtesy of wikipedia, that James I/VI wrote a book on demonology. Never one to let a sound and orderly research programme get in the way of interesting side-projects, I downloaded a copy from Project Gutenberg and started reading. Almost immediately my decision was rewarded, for on the first page of the first chapter of the first book, one of the two people involved in the dialogue (namely, Epistemon) notes that “for as it is said in the logick schools, Contra negantem principia non est disputandum” (p. 4).

Oh! There’s logic in here! That’s an…interesting principle. I’m not sure I’ve heard of it before. I wonder where James found it. Turns out, wikipedia even has an article specifically on this maxim, noting that it is a principle of law and logic, which — nevertheless — is not found in Aristotle. The only medieval citation to it in the article is Duns Scotus’s commentary on Peter Lombard’s Sentences [1]. It’s certainly a reasonable principle, but it’s certainly not a commonly-specified logical principle. Interestingly, in googlebooks, most of the citations I found were from the 19th century, though I did find it in one law book from 1749, The Grounds and Rudiments of Law and Equity, Alphabetically Digested, by a “Gentleman of the Middle Temple”.

Of the remainder of the references I found to this principle in googlebooks, there were four from the 17th C: one in Dutch, one in German, one in Polish, and one in English. There was only one dated from before James’s treatise: Christlicher, warhafftiger Bericht auff und wider die Schmecherten und öffentliche Lügen eines Calvinischen Geistes, der sich nennet Georgium Lupichium Pfarrern zu Ambergk … wider D. Nicolaum Selneccerum …, a pamphlet published in Beyer in 1586, where on the final page, we are told “In Schuelen sagt man: contra negantem principia non est disputandem“.

The topic of “logick/logicque” comes up in one other place in James’s text, and is again found in Epistemon’s speech; he rebuts one of Philomathes’s arguments that there is no such thing as witchcraft or witches with the following:

As to the other reasone, which seemes to be of greater weight, if it were formed in a Syllogisme; it behooued to be in manie termes, and full of fallacies (to speake in termes of Logicque) for first, that that generall proposition; affirming Moyses to be taught in all the sciences of the Ægyptians, should conclude that he was taught in Magie, I see no necessity (pp. 21-22).

So there you have it…logic and witchcraft all in one go.


[1] Joannis Duns Scoti doctoris subtilis, ordinis minorum opera omnia, editio nova, vol. 16, Paris, 1894, p. 93.

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Why do we study medieval logic?


Earlier this week I was up in St. Andrews for the excellent conference on Medieval Logic and Its Contemporary Relevance, a week after coming back from another very excellent conference, on Feminist Philosophy and Formal Logic. The FP&FL conference sparked a lot of thoughts about Who is our audience? that I wrote up for my other blog, but what I found when preparing for my talk in St. Andrews is that a lot of the things that came out in discussion between feminist philosophers and formal logicians are relevant to the study of medieval logic, and why we do it.

Above is a photo of the notes I wrote up for my talk, and I want to use this blog post to recount what I asked my audience: Why do we study medieval logic?

There’s a number of possible answers, of course, and people can have multiple reasons (sometimes all at the same time!). But the answers are all going to fall on a spectrum that has:

On the one end, Pure research/edification: The study of medieval logic is an end in its own right. I feel quite strongly that this is a very good reason to study medieval logic, and it’s one that motivates me quite a bit. There is value in participating in a society where learning for learning’s sake is rewarded, and I think that we should be fighting to maintain such a society: There is no inherent need to justify our study of medieval logic beyond “it is there to be studied”. We study it simply to learn more about it, and that is sufficient. There is no further requirement that we learn from it or that we can apply it or use it or that it has impact in other fields.

Nevertheless, on the other end, Solve all modern problems: We want to cure cancer, identify and block fake news, solve world hunger, etc. Of course, no one thinks that medieval logic can do all this. But we do think that it can do something, that we can do more than just learn about it, we can learn from it, too. But what?

Now some personal confessions: Every paper on medieval logic that I’ve written has contained a paragraphing either (1) explaining why medievalists should care about reading something written in symbols or (2) why modern logicians should care about reading something written in Latin. Every single one. My experience, both in publishing and at conferences, is that (1) is harder than (2), and that this tends to be because medievalists tend to reject formalisms because they are more interested in learning about medieval logic than learning from it, and given that, since they are not versed in modern logical symbolism, having a paper that uses it can prevent them from learning about medieval logic. Broadly speaking, their emphasis is on the “historical” part of historical logic, not the “logic” part of it.

There are a lot of facile answers that can be given for why (2) is easier. One was given in the description of the St Andrews conference itself: Those who do not know their history are doomed to repeat it. This is expressing pragmatic concerns:

  1. Reinventing the wheel is a waste of time: We have a finite about of research energy, we should spend it wisely, doing new things not things others have already done.
  2. Priority: Standards of academic conduct (w.r.t. to plagiarism and attribution, but also with a growing recognition that canon tends to erase certain parts of history, which may result in disproportionately harsh consequences on certain groups of people modernly) require us to attribute results to those who first proved them, and in order to do that we need to know the history of our subject.

But none of this says much about what we can learn from medieval logic — we don’t just study medieval logic so that we can write a proper history of logic. If that were our motivation for studying medieval logic, then we would also be spending more of our time studying non-western logical developments, women logicians, etc. So we still have the question of what we can learn from medieval texts.

More autobiography: I have a relatively stable method for writing papers on medieval logic: I pick an interesting text, summarise its contents, build a formal model, compare it to some modern formalism, and then say something about the result of having done so. What I have to say in what follows is predicated on my own experiences (but people in the audience at the workshop told me afterwards that even if they weren’t in the business of making formal models, what I had to say was relevant for them).

What we (=me) often say in these papers is that we build logical models to offer solutions to modern logical problems (so, not all problems, no cancer-cures, but at least some modern problems), for example:

  • The Liar Paradox
  • Dynamic reasoning
  • Epistemic reasoning
  • Temporal reasoning
  • The nature of logical consequence
  • etc.

But what we can learn from the models depends on who our audience is:

  1. Medieval philosophers/medievalists
  2. Modern logicians
  3. Ourselves

(During the Q&A, someone suggested that I add another category “historians of philosophy”.)

If (1) is our audience, then we have to motivate how modern logic can tell us something more about medieval logic, something we didn’t know before. If (2) is our audience, then we need to be clear regarding how accurate we are being; if our goal is to learn from medieval logic, then this sometimes happens at the expense of the medieval system itself. In these cases we need to be clear when something is, e.g. “Buridan’s logic” or merely “Buridanian logic”. We needn’t be slavish to the medieval texts, if our goal is to take them and learn from them, but when we are not, we must be precise about our deviations.

But if our audience is (3), ourselves, then what do we learn from constructing formal models of medieval texts? For me, the answer is that it teaches me the sorts of questions that I should be asking. The process of constructing a formal model identifies areas where the content needs to be clarified, and where gaps can be found. It’s not so much that the end model gives us an answer to a question but that the process of beuilding the model gives us new questions to ask — both about medieval logic and for modern logic.

A bit more autobiography: At the end of every paper, once I’ve produced my formal model, there’s always a paragraph or two that says “and now given this new temporal operator which the medievals already knew about, I can go forth and SOLVE ALL THE PROBLEMS“. But this is really a bit of a lie: In many cases, I don’t intend to write that “further work” or “future research” paper wherein in I apply the tool I’ve created to some modern logic problem; and I also don’t even worry too much about whether someone else will do it instead of me. For me, the process of modeling is more important than the resulting model itself because of the ways in which it teaches me things, about both modern and medieval logic.

In conclusion, I think that all three of these audiences (four if you add in general historians of logic) should merit our attention, but what kinds of papers we write, and hence what sorts of things we can learn from medieval logic, and what sorts of answers we can give to the question “why do we do medieval logic” are going to depend on which of the audiences is the primary one for any given project. As I argued in the post linked above, I think we don’t always pay as much attention to questions of audience as we should, and that doing so can help us refine and clarify what it is we are doing when we study medieval logic.

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What problem was Ladd trying to solve?

Last weekend I was at an amazing conference on Feminist Philosophy and Formal Logic (which I’ve written about elsewhere), during which there were a number of papers on the history of women and logic. Frederique Janssen-Lauret gave a paper on women in early analytic philosophy, and spoke about Christine Ladd-Franklin’s contribution to logic.

Ladd (as she was at the time) studied at Johns Hopkins under Peirce but was not allowed to formally receive her doctorate. Her dissertation, “On the Algebra of Logic” was published 1883 (and is available from archive.org), and in it, she solved a problem in syllogistic which had purportedly baffled logicians since Aristotle:

The argument of inconsistency
(a\bar{\vee}b)(b\bar{\vee}c)(c\vee a)\bar{\vee}
is therefore the single form to which all the ninety-six valid syllogisms (both universal and particular can be reduced) (p.~40).

I knew a bit about Ladd and her work before Janssen-Lauret’s talk, but this mention of a solution to a long-standing syllogism puzzle piqued my interest immediately — not the least because I wasn’t at all sure what the problem was. As presented, it was a problem about reducing all forms of syllogism to one form, but the idea of “form” here was confusing: Syllogisms are typically spoken of as having mood and figure. Now, “form” here clearly can’t be “figure”, since it is already well-known, and due to Aristotle himself, that every non-first figure syllogism can be reduced to a first-figure syllogism, so the long-standing problem cannot about this sort of reduction, interpreting “form” as “figure”.

If what is meant is, however, “mood”, then the question whether it is possible to reduce all the valid moods to a single valid mood is certainly an interesting one, but I’m not sure that it’s one that has exercised logicians for two centuries — certainly I’d be hard pressed to find a medieval logician who was particularly worried about such a fine-grained reduction, most being content to reduce just to the four perfect syllogisms, Barbara, Celarent, Darii*, and Ferio. So even interpreted in this way, I’m stumped. (And interpreting “form” as something other than figure or mood makes it even more unlikely that the question is one that had bothered logicians for millenia.)

It’s not that I doubt that Ladd provided a solution to some technical problem in the syllogistic — not doubt at all about that — and I’m sure that a precise statement of her problem can be given. What intrigues me here is the social history of the problem: Not what it was but how/when/why did it get recognised as a problem, and how/when/why did people come to think of it as a problem that had plagued logicians since the time of Aristotle?

Looks like I’ve got my next paper topic lined up…

* I very nearly wrote “Dario” here, showing that the distinction between names of syllogisms and names of Game of Thrones characters is not as great as you might think. (Come to think of it, “Bocardo” would be a good name for a roughly-and-tumble pirate warrior, donchya think?)

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Not quite medieval, not quite logic: Proclus’s commentary on Euclid

Earlier this week I was following up on some notes I’d scribbled down over a month ago in a meeting with a colleague, one of which was “Proclus: Image in the water”.

A bit of googling later, and I found myself with a translation into English of Proclus’s commentary on the first book of Euclid’s Elements, along with, per the title page, “A History of the Restoration of Platonic Theology” by the later Platonists, and a translation of Proclus’s “Theological Elements”, courtesy of googlebooks. (Thanks, googlebooks!) Cool! On the face of it, it’s neither medieval nor logic, but it’s definitely something related to both and thus of interest to me.

Someone asked me on twitter who the translator was, and the answer turns out to be…I have no idea. The translator does not name himself on the title page, despite the fact that the publication info is given as “London, printed for the author” and I’m sure that the ‘author’ here isn’t Proclus!, and that there is an extensive preface, where the translator discusses the “great difficulty and labour” that attended his work, arising from the problematic state of his sources. (He laments the “great incorrectness” of the Greek edition and notes that he was substantially assisted by the translation into Latin by Francis Barocius the Venetian, done in 1560. There is otherwise no evidence as to the translator in the frontmatter, and there isn’t much out there elsewhere on google about 18th C translators of Proclus, so I thought I’d take a skim through the book to see if I could find any other clues.

Following the preface there is a “Dissertation on the Platonic Doctrine of Ideas” and after that a “Dissertation on the Demonstrative Syllogism” (!) which includes as part of it a substantial epistemological discussion. This is followed by a third discussion, “On the Nature of the Soul”, and a fourth on “The True End of Geometry”.

These four dissertations concluding, we next have a translation of Marinus’s “Life of Proclus, Or, Concerning Felicity”, and at this point I’m half-way through the PDF and am beginning to wonder just exactly when we’re going to get to the actual texts of Proclus. After Marinus’s biography, the translator gives us a bibliography of Proclus’s works, both available (whether fragmentary or not) and lost. (One of the lost books is a commentary on On Interpretation, which would’ve been really interesting!). Finally, nearly 2/3 of the way through the PDF, we get to Proclus’s commentaries, which comprise the rest of the volume. One can only hope that the next volume has the answer — I shall have to see if I can find it. Meanwhile, I might devote a future post to a discussion of the Dissertation on the Demonstrative Syllogism because it appears to be quite interesting.

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Moody 2018: William of Ockham and his Milieu

From the 2nd to the 4th of March, the University of California Los Angeles will be hosting the yearly Moody Workshop in Medieval Philosophy. This meeting is named after Earnest Addison Moody, a former member of the Philosophy Department and a founding member of the UCLA Centre for Medieval and Renaissance Studies – which are jointly sponsoring the event.

Professor Moody was one of the the pioneers of Medieval Philosophy in North America and one of the first scholars to approach the study of medieval philosophical theories in their own right, without subordinating them to theological views. But for those who have even a passing interest in the history of logic, E. A. Moody is first and foremost the author of  Truth and Consequence in Medieval Logic (19531), one of the most influential volumes in the historiography of medieval logic and of medieval philosophy as a whole.

A Williams College graduate (class 1924), E. A. Moody obtained his PhD from Columbia in 1936, with a thesis on William of Auvergne’s Treatise De anima. While teaching at Columbia, he developed an interest in the history of medieval logic and science. Having retired for a few years to a ranch in Texas, in 1958 he joined the Department of Philosophy at UCLA; there he found a department not only already traditionally strong in logic and language but that was undergoing further changes toward that direction as well – in other words, the perfect fit for Moody’s own research interests.

Above all, those research interest left a significant imprint on the way we look at medieval philosophy in general and at the history of medieval logic in particular, especially in North America. Since the 19th century, the history of the study of medieval philosophy had been almost entirely shaped by quasi-nationalistic and quasi-theological concerns. Leo XIII’s Aeterni Patris encyclical (1879), by restoring “Christian Philosophy in Catholic Schools in the spirit of the Angelic Doctor, St. Thomas Aquinas”, was pivotal in determining a dominant picture of medieval philosophy that had both the kind of uniformity that scholars like Maurice De Wulf ascribed to terms like “scholasticism” and Aquinas as the central figure. True enough, this picture of medieval philosophy as fundamentally homogenous began to break down when Étienne Gilson and others started to realise that it couldn’t manage to account for roughly a thousand years of philosophical speculations. But even so, after Aeterni Patris typically there was still an idea that medieval philosophy had seemingly emerged out of the wreckage of the Roman Empire, grown slowly to a peak with Aquinas, and then began to decay – Gilson, for example, thought that the decay culminated in Descartes. Various people had slightly different pictures, but it was always as a curve and Aquinas was typically at its peak. Now, Moody had a different agenda and a different set of thoughts: he pursued his interests in medieval logic, language and science in connection to the contemporary discussions in logic and language – an whatever Aquinas was up to, an emphasis on logic and language wasn’t really that. This pushed Moody’s interests later, well into the 14th century, and had the consequence that the people who where interested in what Moody was interested in started to look more closely and seriously at the later middle ages, finding in 14th century philosophy a veritable goldmine, while it simultaneously became a common practice to develop those interests in the history of science, logic and language in connection with analogous contemporary endeavours. That ultimately set the tone for Medieval Philosophy on this side of the Pond. E. A. Moody remained at UCLA until his retirement in 1969 and in 1972 was succeeded by Marilyn McCord Adams. Even if McCord Adams later on became much more interested in philosophical theology, when she was at UCLA her major work was on Ockham – and it wasn’t really a theological work at all, rather it focused on Ockham’s logic. Overall, what Moody’s influence in North America amounted to was creating a climate in which Medieval Philosophy could be moved out of theology and toward philosophical issues relevant for contemporary discussions; from that kind of point of view, the 14th century was one of the most interesting things one could study, and in many ways, still is. Nobody else among the major figures who were doing medieval philosophy in Moody’s generation had anything like that on their agenda or achieved similar results.

The Moody Workshop was instituted by Calvin Normore, when he took over the mantle of Medieval Philosophy at UCLA in 1998. The first speaker in the first Moody Workshop was Martin Tweedale, Moody’s last student at UCLA. Since then a small group of scholars meets every year to discuss a particular topic in medieval philosophy, usually among those that would have met Moody’s interest. This year’s meeting, on William of Ockham and his Milieu, is dedicated to the memory of Marilyn McCord Adams.



3:30 PM Peter King (Toronto)
Mental Without the Mind: Ockham’s Radical Revolution


10:00 AM Jenny Pelletier (Leuven)
What is Dominium? Ockham and the Ontology of Lordship

11:30 AM Mikko Yrjönsuuri (Jyväskylä)
Valid on Formal Ground: Burley, Ockham and Buridan

1:00 PM Lunch

2:00 PM Magali Roques (Helskinki)
Ockham’s Theory of Real Definitions

3:30 PM Graziana Ciola (UCLA)
Relativa grammaticalia and the Regimentation of Latin in 14th Century Logic


10:00 AM André Martin (McGill)
What Can the Ockham/Chatton Debate on Self‐Awareness Tell us About Medieval Accounts of Consciousness?

11:30 AM Josh Blander (The King’s College)
Does Ockham Have Priorities?

1:00 PM Lunch

2:00 PM Tom Ward (Baylor)
Ockham on Omnipotence, ‘LogicalImpossibility’, and Hating God

3:30 PM Christopher Martin (Auckland)
Suppose God did not Exist, or that the Eye Were an Animal: Impossible Positio and its use by Scotus, Ockham and Chatton


If you happen to be around, come and join us!

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Three-year lectureship in medieval philosophy, Charles University, Prague

Boosting the signal:

Job offer: Lecturer in philosophy
Department of Philosophy and Religious Studies
Faculty of Arts, Charles University

The Department of Philosophy and Religious Studies, Faculty of Arts, Charles University invites applications for one full-time three-year position at the lecturer level (starting at AP2 in the Czech scale), beginning October 1st 2018.

Info about the department: http://ufar.ff.cuni.cz/10/about-our-department

The area of specialization for the position will be medieval philosophy possibly with another area of specialisation.

Responsibilities for the position include:

  • teaching philosophy courses at the undergraduate as well as graduate level: 7 courses (course = 90 min per week) in one academic year (academic year = two terms), i.e. 3 courses in one term, four courses in the other term
  • supervising students
  • student’s examination
  • contributing to the curriculum development as appropriate
  • establishing and maintaining independent research
  • participating in the academic life of the department


  • PhD in philosophy or a related field
  • teaching experience
  • publication record
  • working knowledge of Latin (the curriculum includes Latin reading classes)
  • excellent command of English (or Czech) both in writing and speaking; knowledge of Czech is not required but working knowledge of it is expected after two years (in the case the contract should be prolonged); good knowledge of one other language (preferably German or French)

Conditions of employment

The Faculty of Arts offers a salary up to 30 000 CZK with possibility of further increase depending on the research outcomes of the employee. The Faculty covers social and medical insurance according to EU regulations. According to the university rules the contract can be prolonged after three years; the prolongation is either for another period of three years or tenure. The probationary period is three months.

Starting date: 1st October 2018


You may apply for this position until 15th March 23:59h / before 16th March 2018 Prague local time. Submission by mail or in person: the application with all its attachments can be sent by mail or delivered in person to the following address: Hana Vamberská, Human Resources Dept., FF UK, nám. Jana Palacha 1/2, 116 38 Praha, Czech Republic

Submission by e-mail: the application with all its attachments can be sent by e-mail to the address hana.vamberska@ff.cuni.cz.

The application must include the following:

  1. a cover letter containing your motivation for the position
  2. cv and list of publications
  3. the names and contact details of two referees and an indication whether we can contact them at this stage
  4. a sample of a written work that is relevant to this position, not more than 10 000 words; it may be a published or unpublished sample and may be an extract from a longer piece
  5. teaching evaluation (if available)
  6. suggestion of a syllabus for an undergraduate course on medieval philosophy (two terms, 20-24 lectures (one lecture = 90 min); the aim of the course should be introduction to medieval philosophy (possibly its sources and impacts on later tradition) for philosophy students on BA level

The application process will be in two rounds. The committee appointed by the dean of the Faculty of Arts decides in the first round on the basis of submitted materials. The candidates invited for the second round will be asked to (a) deliver a public lecture in the Department of Philosophy and Religious Studies, Faculty of Arts, Charles University and (d) be available for an interview with the committee.

The shortlist of candidates for the second round will be available by early April 2018; lectures and interviews are scheduled for late April and early May 2018.


For additional information you can contact:
Dr. Jakub Jirsa, Head of department, jakub.jirsa@ff.cuni.cz (job profile and academic matters)

Hana Vamberská, hana.vamberska@ff.cuni.cz (application procedures)

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Brill’s “Investigating Medieval Philosophy” series

In case any of our readers don’t already know about it, Brill has a book series “Investigating Medieval Philosophy”, edited by John Marenbon and with an editor board: consisting of Margaret Cameron, Simo Knuuttila, Christopher J. Martin, and our very own Martin Lenz. The series aims to publish two volumes a year, and:

The series aims to provide a peer-reviewed forum for high-quality monographs and coherent collective volumes on medieval philosophy, written in such a way as to make them comprehensible and interesting to mainstream philosophers and historians of philosophy in Anglophone philosophy departments. Volumes in the series are not required to use medieval philosophy to make a direct contribution to debates in contemporary analytical philosophy (although this is one possibility), but the manner in which the medieval texts are treated should reflect, in an historically sensitive way, the methods and the language of contemporary analytical philosophy – in especial, its ideals of clarity and unpretentiousness. There are many different varieties of this general ‘analytical’ approach, and the series is open to any of them. The scope of medieval philosophy is taken widely, to include the Arabic, Greek and Jewish traditions, as well as the Latin one, and to run from c.500 to c.1500; works which go on even so far as 1700 may be considered, if they are at least equally concerned with the period before 1500.

For more information, including titles in the series, see here.

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