1. Every goat is an animal → Some animals are goats: valid.
2. No stone is a tree → No tree is a stone: valid.
3. Some teachers are poets → Some poets are teachers: valid.
4. Every fish is an animal → Every animal is a fish: invalid.
5. Some animals are not birds → Some birds are not animals: does not follow.
6. No goat is a horse → Some horses are not goats: not the specified standard converse; use No horse is a goat.
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Six self-check examples
Simple Conversion of Propositions: Definition, Method and Rules
1. Every goat is an animal → Some animals are goats: valid.
2. No stone is a tree → No tree is a stone: valid.
3. Some teachers are poets → Some poets are teachers: valid.
4. Every fish is an animal → Every animal is a fish: invalid.
5. Some animals are not birds → Some birds are not animals: does not follow.
6. No goat is a horse → Some horses are not goats: not the specified standard converse; use No horse is a goat.