Biconditionals and the structure of a definition
- Writing a definition for a made-up word — 3 tasks
- Surviving the examples is not being right — 3 tasks
- A definition runs both ways — 3 tasks
- Join it, or refuse — 3 tasks
- Going Deeper — 3 tasks
- Practice — 26 tasks
- Summary — 2 tasks
- Cool-down — 3 tasks
Classroom activities
Things a class does rather than writes on. Each one is a finished PDF: print it, cut it up if it says so, and hand it round.
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Join It with If and Only If, or Refuse? — Cut & Glue Sort 25 minutes · 5 sheets
12 if-then statements. Students check each statement and its converse, then glue it in one of three rows: join them, do not join (the converse is false), or do not join (the statement is false).
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Which One Has a True Converse? — Maze 10–15 minutes · 4 sheets
8 boxes, each with two true if-then sentences about angles, midpoints, bisectors and lines. Only one has a true converse and can be joined with if and only if.
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If and Only If: True Both Ways? — Mystery Picture 25–35 minutes · 4 sheets
25 if-and-only-if sentences about angles, midpoints, bisectors and lines. Students check each one forwards and backwards; the true ones make a picture.