Latest Book: Introduction to Plausible Reasoning

Click here to purchase on


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





Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s