Free practice · single-choice · hard

Practice

Find a converse counterexample

The rule is: if a package is express, it has a blue label. Which possible fact disproves the claim 'every blue-label package is express'?

Deduction chain

Preserve direction from premises to conclusion

  1. PremisesSeparate facts and rules
  2. DirectionMark if, only, all, and some
  3. ConnectLink matching terms
  4. ChallengeTry a counterexample
  5. ConcludeState only what is guaranteed

A guaranteed conclusion follows only when stated facts activate rules in their written direction and no counterexample survives.

Choose one answer