Bruce Thompson's Fallacy Page



This website presents my attempt to make sense of the bewildering subject of bad reasoning. Many philosophers have attempted to name and classify types of fallacies, but no list or classification scheme has so far managed to be comprehensive. This list is also incomplete. In fact, I believe any list of fallacies must necessarily be a work-in-progress, since the use of fallacious reasoning is itself constantly changing. The fallacies that were well-known to the ancient Greeks and Romans were the fallacies used by the politicans and orators of the day. We still have politicians and orators today, so those fallacies are still with us; but we also have to keep track of fallacies used by advertisers and the news media. With the advance of science we have had to keep up on the fallacies involved in scientific (and pseudo-scientific) reasoning. As new public institutions emerge, no doubt new forms of fallacious reasoning will arise with them. We logicians need to stay alert.


On this page you will find...

1. A DEFINITION of the term "fallacy," and a discussion of the nature of fallacious reasoning.

2. An explanation of the PRINCIPLES that I use to classify and organize fallacies.

3. A table on which the FALLACIES are organized according to their classification.

Click on the class name for a list of fallacies in that class. Click on each fallacy to see an explanation of that fallacy, a couple of pithy examples, a discussion of why we sometimes find that fallacy to be persuasive, and a source indicating who first described and/or named the fallacy, if such an original source can be identified.

4. Lots of EXERCISES to give students practice in identifying fallacies, broken into convenient units.

5. A BIBLIOGRAGHY of print sources and websites.

6. An INDEX in which fallacy names and other terminology are listed in alphabetical order, with appropriate hyper-links.


A Warning to the Uninitiated and a Plea to Fellow Aficionados

Those who are looking for an authoritative list of fallacies will not find it here...or anywhere else for that matter. The study of fallacies--although it is well over two thousand years old--has not so far resulted in a catalogue of fallacies that could be considered in any way comparable to the catalogues of plant and animal species that biology has provided us with. Instead we find that no two scholars offer the same list of fallacies. There is very little agreement even on the categories into which fallacies can be divided. Where the same fallacy appears on different lists, it is often called by a different name.

This state of affairs may be due, in part, to the nature of the subject matter itself. Instances of fallacious reasoning are not quite like biological specimens, although they can be observed in the wild and collected for examination. But, biological specimens can only be collected in the wild; instances of fallacious reasoning can be (and usually are) invented whole cloth by the scholars who study the subject. Hence, scholars unhappy with the available real-life examples that instantiate a fallacy on his list can remedy the situation by inventing made-up examples that exactly fit his concept. I use this technique myself, so I am not in a position to complain; but, that this method is available to scholars suggests that the study is not as scientific as we might wish.

However, the sorry state of fallacy scholarship, which was first noted by C. L Hamblin in his 1970 book Fallacies, cannot all be blamed on the difficulty of the subject matter. Much of the blame can be laid at the feet of those of us who teach and study the subject. The study of fallacies has, I believe, suffered enormously from a lack of basic scholarly methodology. One scholar will use another scholar's label without giving any attribution, on the assumption that the names of fallacies are all in "common usage," making basic scholarly citation unnecessary. In fact, many of the names of fallacies may have grown out of common usage, and may have no other origin than the observations of anonymous speakers; but, in many other cases, the labels were coined at a specific time, by a specific philosopher, for a specific purpose or to cover a specific example or group of examples. In some cases these coinages have since entered common usage; in other cases, not. In any case, because these origins generally go undocumented by teachers and text books, every list of fallacies, however informal or hastily drawn up, presents itself to students as an authoritative list handed down in the same form for untold generations, perhaps going back to the Garden of Eden itself. After Adam named the various animals, he then named the fallacies! Students come away from a logic class thinking they have "learned fallacies," when they have in fact only learned one list of fallacies. What they take to be a complete, comprehensive, uniform and authoritative treatment of the subject was in fact incomplete (due to the nature of the subject), merely introductory, rife with idiosyncracies, and utterly lacking in basic scholarly methodology!

What's to be done about this? Here are my suggestions:

1. The subject itself should be presented to students as an on-going enterprise (into which they are welcome to enter). They should be made aware of the fact that there are no standard lists; that scholars disagree among themselves on principles of organization, on the labels they give to the fallacies, and even on such fundamental matters as how to define the term "fallacy." Properly forewarned, students can then enter the study with an appropriate degree of trepidation...and an appropriate understanding that this is a field in which their own contributions may make a difference.

2. As an on-going enterprise, scholars (by which I mean "students") must be allowed to contribute new labels and new descriptions, thus resulting in expanded lists. However, such additions should be made circumspectly. I suggest that scholars should always try, where possible, to fit new examples into already recognized pidgeon holes. Where this is not possible, scholars should take credit for coining new names. This is so future scholars can document the source of the name, if they choose to adopt it onto their own list. Finally, a new fallacy should be added to a list only if there are real-life examples of the fallacy. Made-up examples are not sufficient. We should be able to cite the author, date, and occasion of an error if we think it is important enough to add to a list.

3. We should adopt the habit of citing or documenting the source of the fallacies on our lists. Even if the original source cannot be authoritatively identified, we should at least indicate where we got the name from so that we can begin to document when the name came into common usage and approximately how old it is.

4. Within reason, and where possible, we should try to adopt scientific standards on naming. The convention among biologists is that the oldest name should be adopted as correct. That is why we no longer have a dinosaur named "brontosaurus." It would be nice if lists of fallacies could be drawn up on a similar principle, since this would eventually result in more or less standard lists. However, this may not be possible. In some cases it may not be possible to establish which name is oldest--precisely because scholars in this field have traditionally been so sloppy about documenting the source of names! Also, oldest may not be best. Perhaps, following the practice of lexicographers, we should adopt the name that has the widest range of common usage. Perhaps we should adopt the name that is pedagogically superior, i.e. that students have the easiest time remembering. (This would be an argument for replacing the name "secundum quid" with the name "reverse accident." "Secundum quid" is documentably the oldest name, but "reverse accident" is generally preferred by my students.) I am not sure what principle we should adopt. I address the problem by trying to mention all of the alternative names of which I am aware.

On this page, I have tried to follow these policies. I call the page "Bruce Thompson's Fallacy Page" specifically to warn students that this is my list, not the official list that descends from the Garden of Eden. Every fallacy on the list includes some indication of its source, either the documentable original source or, at the very least, my personal source, i.e. the oldest occurrence of which I am aware. In some cases I have added fallacies to this list that do not appear on any previous list. When I do so, I take credit for the addition, and try never to add a fallacy to the list unless I can cite examples of its use in public discourse.


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