Latest Book: Introduction to Plausible Reasoning

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This book was originally intended for my senior Theory of Knowledge students of the International Baccalaureate at Father Michael McGivney Catholic Academy, in Markham, Ontario. That is why I intended to add as a subtitle: “For IB Theory of Knowledge Students”. Later on, I began to deliberate on other possible subtitles: “For Seminarians”, or “For Priests and Seminarians”, etc. Eventually I had to drop the idea of a subtitle that narrowly circumscribes my target audience; the reason is that people in general are unfamiliar with the fundamentals of plausibility theory, which is evident in the very tone of their overconfident and dogmatic rhetoric, especially when spouting off on political, foreign policy and economic matters of which they know very little. This short treatise is really intended for anyone who is interested in a basic introduction to the fundamentals of plausibility theory and some of its epistemological implications. I am hoping that it is a good stepping-stone to other more sophisticated treatments of this area of philosophy.

For a time, I was teaching my students an inductive logic that was fundamentally probabilistic, i.e., Bayes theorem and frequency type probabilities, along with their implications for knowledge. After a while, however, I was becoming less and less convinced that probability was the model that properly accounts for the way we reason inductively, for example in jury deliberations. I became increasingly convinced that Nicholas Rescher’s account of plausible reasoning was far more true to the basic logic of the scientific method and our day to day reasoning. The difficulty, however, was finding a way to make his thought intelligible not only for my young students, but for friends and colleagues, in particular seminarians studying for the priesthood, not to mention priests who have only been introduced to the categorical logic of Aristotle during their seminary days. It has been my impression that their exposure to this classical logic and this logic alone may account for the lack of awareness—in quite a number of them today—of the underdetermination and tentativeness of many of their contentions and the dogmatism that often ensues, which in turn can spawn a very off putting clericalism.

In terms of the mechanics of plausibility theory, there is nothing entirely original here—I am borrowing heavily from the writings of Rescher, in particular his Plausible Reasoning: An Introduction to the Theory and Practice of Plausibilistic Inference. His ideas are ideal for IB Theory of Knowledge students, but his works are somewhat beyond their reach. My task is to extend that reach and thus enable them to eventually explore more deeply the intriguing and important ideas of this great American philosopher. If this book helps a young student write a decent TOK essay on one of the six titles prescribed for them every year, or if it helps anyone who reads it to appreciate more fully the limits of human knowing, the evolutionary and communal nature of truth possession, and thus the need for continual dialogue with others who see things from an entirely different vantage point, then I have succeeded in what I have set out to do.


Table of Contents

Copyright Page



Author’s Biography

1  Introductory Thoughts on the Importance of Plausible Reasoning

2  Deductive Certainty

3  The Logic of Uncertainty

4  Introduction to Propositional Logic

Exercises (Truth Tables)

5  Some Basic Rules of Inference

6  Sets, Subsets, and Inconsistency

7  Plausibility Values

8  Maximal Consistent Subsets

9  Plausible Reasoning

Exercise: Hit and Run Scenario

10  Plausibility Analysis of the Murder of Dorothy Donavan

11  Information and Truth Status

12  Systems and the Tentative Nature of Truth

13  Some Epistemic Implications

14  Interpretation and Perspective

15  Questions and Cognitive Dynamics

16  Empirical vs. Paradigmatic Thinking

17  Knowledge as Map

18  Introduction to Some Epistemetrics

19  Confidence Thresholds and Some Cognitive Biases

  1. Some Final Reflections: Theological and Moral

Appendix A: Exercises (Answers)

Appendix B: Exercises (Answers for Hit and Run Scenario)

Suggested Reading





Readings in the Theory of Knowledge (Revised and Enlarged Edition)

Preface to the Second Edition


As I said in the preface to the first edition of Readings in the Theory of Knowledge, this book began as a series of short essays specifically written for my Theory of Knowledge students in the International Baccalaureate program at Father Michael McGivney Catholic Academy. Since publishing the first edition, I have continued to write short essays for them, primarily to make matters somewhat easier for them—the prescribed titles from which they choose a title for their TOK essay are still very lofty, perhaps a bit too lofty for high school students. I have used these new articles in class over the years and knew that I would include them in a second edition if I ever got around to writing one. This work is a revised and expanded version of the previous work. The font has been increased to 12, thanks to the complaints of some of my students, and I have added some new chapters, specifically on necessary and sufficient conditions, independent and dependent variables, Jeffrey’s Rule and what this rule might imply with respect to rumors, Burley’s Rule and moral integration, a revised chapter on Inference to the best explanation, which, thanks to Nicholas Rescher, I now refer to as Inference to the Best Estimation; I also added a short introduction to plausible reasoning. These last two revisions were the result of discovering the writings of Nicholas Rescher; one day after school, shortly after publishing the first edition, I wanted to read something on ignorance, so I did a quick search on Kobo and found a book entitled Ignorance: On the Wider Implications of Deficient Knowledge, by Nicholas Rescher. Discovering Rescher gave me a new lease on teaching. I decided not to retire, but to study many of his writings and to find a way to make his thought accessible to my students. I’ve included only a tiny portion of the things I’ve put together for my students; the rest I reserve for a separate book to be entitled: An Introduction to Plausible Reasoning.

One of my principal goals in publishing the first edition was to have students come to a genuine appreciation of the scope of uncertainty in the pursuit of knowledge, especially with respect to their day to day inferences. That remains my goal, because things have not changed all that much in this regard. In fact, dogmatism has intensified. Knowledge is very difficult to acquire, and good thinking is about bringing maximal and consistent plausibility to our own epistemic framework (the set of data through which we interpret the world around us). As new data (or theses) are added to our existing set of data, the plausibility of much of that information changes and, if we are honest thinkers, we try to re-establish coherence and maximal consistency to that new data set. That will involve discarding theses or data that are inconsistent with new data that has greater plausibility.

This epistemic process is an ongoing one, which is why some of us—those who make the effort to think—change our minds very often throughout our lives. Science is a matter of plausible reasoning, which is why the history of science is evolutionary and revolutionary (the history of science is, among other things, a veritable graveyard of discarded hypotheses). So too is philosophy an evolutionary process—although the history of philosophy has had a very different kind of trajectory. All knowledge is subject to the same evolutionary law.

One important lesson to take away from this fact is the importance of avoiding the habit of “over-stating your case”. We do not always know for certain whether our data is correct (most often, the plausibility index of the data on which we ground our conclusions is less than certain), nor do we ever know whether we have enough information and whether the plausibility of our current conclusions will change as a result of additional information in the future, etc. Hence, the importance of cultivating a certain degree of epistemic humility. But the spirit of dogmatism—that stubborn unwillingness to examine new data for fear of upsetting the applecart of one’s own conceptual framework—is alive and well in the world, especially among those who see themselves as open-minded progressives. This is ironic, because we seem to pride ourselves on being an open society. We are very far, however, from being the open society we imagine ourselves to be. We are not critical thinkers until we begin to question the plausibility of our sources, reject outright the epistemic hubris that characterizes so many talking heads and political pundits in mainstream media, and learn to suspend our disbelief. This book aims to help further that end among young people.