MEPX
Chapter 2 of 10All chapters
  1. 1What an argument is
  2. 2Validity and soundness
  3. 3If, then
  4. 4All, some, none
  5. 5Necessary and sufficient
  6. 6Deduction against induction
  7. 7Formal fallacies
  8. 8Informal fallacies
  9. 9Logic puzzles
  10. 10Using it in real arguments

Chapter 2 of 10

Validity and soundness

Two different questions.

Validity is structural

An argument is valid when true premises would force the conclusion. It says nothing about whether the premises are actually true.

  • All fish can fly; salmon are fish; so salmon can fly. Valid, and nonsense.
  • Invalid arguments can still have true conclusions, by luck.

Soundness

A sound argument is valid and has true premises, which is what you actually want. In practice most disagreements are about premises, so attacking the logic often misses the point.