MEPX
Chapter 9 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 9 of 10

Logic puzzles

Deduction under constraints.

Grid puzzles

Given clues that link categories, mark what is impossible rather than what is true. Certainty usually arrives from elimination, and each new fact makes earlier clues say more.

  • A yes in one cell means no across its row and column.
  • Reread the clue list after every deduction.

Knights and knaves

When some speakers always lie and others always tell the truth, assume one case, follow it to a contradiction, then try the other. Systematic case analysis beats intuition.