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Chapter 2, Implication Rules
One Versus Two Way Implications
Previous Section: The Second Puzzle
The two puzzles give examples of implication rules. The first puzzle gives a
one-way implication rule, while the second gives a two-way implication rule. The
following words should further help you to see the difference between one- and
two-way implication rules. Seeing this difference may help you understand better
the answers to the above questions. They may also help you answer the five
questions again using the two-way implication rule.
- A one-way implication rule says that when a first situation occurs, so
must a second. It does not say that when the second occurs so must the
first. The second situation may occur without the first.
- A two-way implication rule says that
- when a first situation occurs, so must a second, and
- when the second situation occurs, so must the first.
A two-way rule says that when each situation occurs, so must the other.
Therefore if the two-way rule is to be obeyed, when one situation does not
occur, neither can the other.
Seeing or recognizing the difference between one- and two-way implication
rules makes you a more careful thinker.
One- and two-way rules, recognized or not, are what we use to reach
conclusions or make judgments. One and two-way rules can be used to suggest or
persuade us of what needs to be done or avoided.
Chapter Sections: [ 4. First Puzzle ] [ 4. Second Puzzle ] [ 4. IF versus IFF ] [ 4. Joking About Logic ] [ 4. Imply or Suggest ] [ 4. One vs Two-Way Committents ] [ 4. Repeat- & Reproduc-ible? ] [ 4. Rules Limits & Benefits ] [ 4. Accidental Rules ] [ 4. Steps for Better Reason ]
Next: Talking About Logic
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