Fallacies: Twitter Roundup

I’ve written up a number of things about fallacies for posting on Twitter (since people regularly accuse anyone they disagree with of this or that fallacy, with a breathtaking ignorance of fallacies and fallacy theory—which they believe is some kind of settled part of logic, seemingly).

Well, today I’m going to be lazy and just post a bunch of my various Twitter images here, for what they are worth.  Enjoy!

Only arguments can be fallacious. Where there is no argument, there is no fallacy:



People do not understand that material fallacies or informal fallacies are informal precisely because they are fallacious only sometimes, depending on their content. They think they are always fallacious, which is silly:



Correcting a Mistake on my Part

In the image above, I said that any argument that instantiates the form of a formal fallacy is therefore invalid. I used denying the antecedent as an example of a formal fallacy.  Now, denying the antecedent is indeed an invalid argument form 

  1. P ⇒ Q
  2. ~P
  3. ∴ ~Q

but I was WRONG to say that “any argument that instantiates an invalid argument form is invalid.” This is not the case—even though many people think it is the case, including me when I wrote the above, simply because I had never sufficiently inquired into fallacy theory, something I have done a good deal more since writing that.

The correct principles are “an argument is valid IFF it instantiates any valid argument form” and “an argument is invalid IFF it instantiates NO valid argument form.” That an argument instantiates an invalid argument form does not show that the argument is invalid. Consider:

  1. If God created anything then God created everything.
  2. God did not create anything.
  3. ∴ God did not create everything.

This argument instantiates the invalid form of denying the antecedent. Yet it is a valid argument. How do we know it is valid? If the premise are true, it is not possible for the conclusion to be false. That is what a valid argument JUST IS. The fact that the argument ALSO happens to instantiate an invalid argument form entails nothing at all about the validity of the argument. An argument can in principle instantiate as many invalid argument forms as one wishes—so long as it also instantiates just one valid form, it is a valid argument.

A common sense way to think about it is to look at an argument as a movement of the mind from the premises, A, to the conclusion, B.  There is either a way to get from A to B or there is not. If there is ANY route by which you can get from A to B, then there is a way to get from A to B. It doesn’t matter if there are dozens or hundreds or thousands or billions of routes that won’t get you from A to B; all you care about is whether there is at least ONE. If there is at least one route from A to B, then you can get from A to B. The only way in which you cannot get from A to B is if there are NO routes from A to B.

In sum: that an argument instantiates an invalid argument form doesn’t show the argument is invalid. It doesn’t show anything.




Anyone who frequents Twitter or the comments of YouTube will have encountered the dreaded Online Fallacy Sperg:


Since fallacies are just errors in reasoning that happen commonly, I’ve identified and named a few of my own:


I have a full post about the All True Scotsman Fallacy.  Please read it.  It does a much better job than this card does (although the card makes the interesting point that if the “No True Scotsman” were a fallacy, any predication of anything to anything would be fallacious.




I also have a have full blog post about this one, the Burden of Proof Fallacy.  I also have a humorous treatment of it in my Burden of Proof Fairy post.


And finally, a long piece from the Stanford Encyclopedia of Philosophy detailing why fallacies and fallacy theory are far from being a settled part of logic, but are in fact a very problematic area, with one position (to which I am starting to lean) being that there literally are no such things as fallacies. I’ll be blogging further about this position and the arguments for it in future.


And to end, words of wisdom, as always, from G. K. Chesterton:



One comment on “Fallacies: Twitter Roundup

  1. tryanmax says:

    I like the tennis analogy. It is a very good point that few things are taught by labeling and responding to common errors in the field.

    Case in point, the (my) field of graphic design has no terms for bad design besides “bad design.” One might say this is because graphic design is a highly subjective discipline, but subjectivity has it’s limits. If a design “doesn’t work” in the sense that it in the majority of cases causes confusion rather than elucidation, or that it fails to persuade, or that it is simply unpleasant to look at (assuming that is not the desired effect), it is “bad design” in a very real sense.

    In sum, one need not formalize the identity of errors in order to avoid them. Better to formalize the principles of what’s good (for which there are many terms in design) and encourage the student and practitioner to strive for those.


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