The premises must have certain characteristics: one must be universal and the other particular. This means that during this reasoning we start from the broad or universal statement (first premise), then the most particular idea is taken into account, which helps to contrast the first premise, and thus a conclusion is obtained.
Rules of syllogism
What you want to avoid with this reasoning is that the conclusion is a fallacy, that is why the following rules must be met:
- The fixed structure of the syllogism is: two premises, one universal and one particular, and a conclusion.
- The particular premise cannot be the conclusion at the same time, nor can it be contained in it.
- There must always be a universal or greater premise, because a logical conclusion cannot be reached starting from two particular premises.
- The conclusion must be particular, and not as universal as the first premise.
- A conclusion cannot be drawn if the premises are negative.
- A negative conclusion cannot be drawn from affirmative premises.
- The premises must have common terms.
- The conclusion must express themes related to the premises.
Consequences of breaking the rules
- Semantic ambiguities. It is generated when the premises can be interpreted in various ways, preventing the terms from being clear and therefore the deduction could not be correct.
- Paralogisms . Errors in the deduction that are ignored, since they formally appear to be valid, but no.
- Sophisms . It is when the person in charge of deducing the conclusion creates false reasoning intentionally to manipulate.
- Subject ignorance. It is when impossible conclusions are affirmed. This occurs if you use weak or buggy premises.
- Generalizations . A particular conclusion cannot be carried into broader fields.
Examples of syllogisms
- All men are free
- Jaime is a man
- Jaime is free
- Some birds are white
- I like white animals
- I like some birds
- No man can live under water
- Fish live under water
- Fish are not men
- The planets are all round
- Mars is a planet
- Mars is round
- Owning a private jet is for millionaires
- Chris has a private jet
- Chris is a millionaire
- No fish is mammal
- Dolphins are mammals
- Dolphins are not fish
- Some snakes are poisonous
- Poisons can kill us
- Some snakes can kill us