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Formal validity

This step introduces the key idea of formal validity: validity in virtue of logical shape or form.
a pair of formal black lace-up men's shoes
© University of York

We’re going to look now at a further sharpening of focus for our project. One that will bring us closer to giving a systematic account of good reasoning.

Take a look at the following (very simple) arguments.

Argument 1

  • Mattie is tidying or Mattie is gaming online
  • Mattie is not tidying
  • So, Mattie is gaming online

Argument 2

  • A new welfare system will be introduced or levels of child poverty will increase
  • A new welfare system will not be introduced
  • So, levels of child poverty will increase

Argument 3

  • Tom is fun to be around or Tom is a logician
  • Tom is not fun to be around
  • So, Tom is a logician

These arguments concern radically different subject-matter, but all of them seem to be valid. (For each one, if its premises are true, its conclusion has to be true.) But they have more in common than just being valid. All three arguments seem to have a similar structure, shape, or form. Further, it at least seems plausible that what makes these arguments valid is that they have this particular shape or form. As we’ll say, it looks like they are formally valid.

Let’s look more closely at these ideas.

© University of York
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Logic: The Language of Truth

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