The Easy Case for Dialetheism: Timmy the Square Circle and Divaltopian Law

Dialetheism is the view that some contradictions are true. Put another way, dialetheists claim that there are propositions that are both true and false at the same time and in the same respect.

For many people, this is plain crazy. Others find it extremely counterintuitive but will grant it because they’ve heard quantum mechanics proves it. Others still may suspect it is a desperate response to certain logical paradoxes, such as the Liar.

I wish to argue that all of this is quite beside the point. I don’t understand quantum mechanics (at all), but I would be surprised if there were really no way to account for experimental data without recourse to true contradictions. I’m (somewhat) better versed in debates about logic. I can tell you with confidence: the paradoxes have plenty of coherent solutions. Philosophers disagree primarily on the relative costs and benefits of these solutions. If dialetheism were truly incoherent and demonstrably impossible, we wouldn’t be backed into it: cheaper options than insanity are for sale.

There is a much simpler reason to be a dialetheist: despite initial appearances, it is intuitively compelling and even quite obviously true. We need no special training in physics or logic to see this.

Before getting on with the argument, a quick clarification about a misinterpretation of dialetheism that I encounter alarmingly often: dialetheism is the view that there is at least one true contradiction. It is not the view that all contradictions are true. That view is actually nuts. For example, that my name is William Nava is only true, it is not also false.…

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What Is Logic Selection? Part II: The Selection Process

Graham Priest

In Part 1, we disambiguated between the logic that we intuitively use (hereafter “intuitive logic”) and systems of logic. Systems of logic codify a set of rules of entailment. That set of rules may or may not accurately represent the rules involved in intuitive logic. Logic selection is the process of finding a set of rules that does.

You might think of it this way: there are many systems of geometry. There’s traditional Euclidean geometry, but there are also various non-Euclidean geometries. No one of them is any more a geometry than any other. To choose between these geometries, we need to match up their rules against what happens in the type of space we want them to represent.

So it is with logic. To choose a system of logic, we need to match its rules of entailment against the rules of intuitive logic.

Of course, the process of logic selection cannot be a merely logical one. That would presuppose what we’re looking for. We can (must) use intuitive logic in the selection process, as we use it in all our reasoning. But we can’t use any formal system of logic. So, what do we use?

The selection criteria

Logician Graham Priest presents a theory of logic selection in this video. Priest argues that the process of theory selection is always the same, whether you’re selecting a theory of logic, physics, or economics. The selection criteria are as follows:

  • Agreement with data
  • Simplicity
  • Internal consistency
  • Power (how much data it accounts for)
  • Relevance (avoidance of the ad-hoc)

Agreement with data is always the most important criterion.…

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