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Necessary and Sufficient

Necessary and Sufficient


Assumptions can sometimes be discovered in gaps in arguments about whether conditions exist to draw a specific conclusion. Identifying whether support exists in the argument for either necessary or sufficient conditions can be a useful skill for students to learn.

The activity

This activity is simple, and consists of giving students a premise and a conclusion and asking whether the premise by itself contains:

(a) a necessary condition for the conclusion

(b) a sufficient condition for the conclusion

(c) both necessary and sufficient conditions for the conclusion

(d) neither necessary sufficient conditions for the conclusion


Premise: John was driving 55mph in a 30mph zone

Conclusion: Therefore, John got a speeding ticket

Answer: This is a necessary but not sufficient condition, as there must also have been a police officer there to observe and give the ticket.


This is most effective when the premises and conclusions are generated from your course content.


Combine this with a Think-Pair-Share or make the scenario very detailed and combine it with a Four-S activity to increase the level of social engagement.

Adapted from: Van Den Brinkbudgen, R. (2000). Critical thinking for students: Learn the skills of critical assessment and effective argument (3rd Edition). London: How to Books.

Framing this activity for success


For this reason, frame each activity using these four steps:


Important: Wait Five Seconds!

