Syllogisms: Possibility and Reverse
advanced28 min read
The harder syllogism variants — 'is a possibility' conclusions, reverse syllogism where you pick the statements that force a given conclusion, and chains of three or four statements. All handled with Venn diagrams drawn as labelled regions.
What you will be able to do
- Decide whether an arrangement described by a 'possibility' conclusion can be drawn without breaking any statement.
- For a reverse-syllogism item, test each candidate statement set for whether it forces the target conclusion.
- Work a chain of three or four statements by composing the containments step by step.
- Separate a definite conclusion from a mere possibility.
What is inside this lesson
- 1Three harder variants
- 2What 'a possibility' means
- 3Testing a possibility conclusion
- 4Reverse syllogism
- 5Chains of three or four statements
- 6Worked examples
- 7Common mistakes
- 8Quick revision
- 9Practice
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Three harder variants
Once you can test a plain syllogism with a Venn diagram, three variants raise the difficulty:
- Possibility conclusions — 'All A being B is a possibility.' You are asked whether such a picture can be drawn without contradicting the statements.
- Reverse syllogism — the conclusion is fixed and you choose which set of statements would make it follow.
- Longer chains — three or four statements that must be composed in order.
Every one is still solved by drawing regions, not by reciting rules.
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