Syllogisms Below are 20 logic puzzles known as syllogisms. Each syllogism is made up of two premises followed by a conclusion. conclusion. For each syllogism you must decide whether the conclusion is valid or invalid by determining whether it follows logically from the premises without the need for any other information. information. The average score is about 10 to 12 correct out of 20. A brief explanation explanation and the answers can be found at the bottom of the page Example: Premise 1: All cats are mammals Premise 2: All mammals are animals Conclusion: Therefore all cats are animals 1
All of of th the pu purple cr cravats ha have bl blue po polkadots Some of the ties are purple cravats Therefore some of the ties have blue polkadots
2
All ne neurosurgeons ar are hi highly in intel telligent Some neurosurgeons are not gentlemen Therefore no gentlemen are highly intelligent
3
Some computers are not laptops Some laptops are not MacBooks Therefore some computers are MacBooks
4
No people tell lies Some psychology students tell lies Therefore some psychology students are not people
5
Some daily newspapers are tabloids No textbooks are daily newspapers Therefore no tabloids are textbooks
6
Some green things are not plants All green things are trees Therefore some trees are not plants
7
All ra rats in Lo London ha have co contag tagious di diseases Some rodents have contagious diseases Therefore some rodents are rats in London
8
Some types of bird are kept as pets All things kept as pets are goldfish Therefore some goldfish are types of bird
9
Some woolen cardigans are not trousers Some trousers are not shirts Therefore all shirts are woolen cardigans
10
No fish are rainbow trout All rainbow trout are salmon Therefore some salmon are not fish
11
All habi abitua tual fa failure lures s are are life life's 's losers sers None of life's losers are unhappy people Therefore some unhappy people are habitual failures
12
No shin shiny y red red appl apples es cont contai ain n dead deadly ly pois poison on Some types of fruit contain deadly poison Therefore some types of fruit are not shiny red apples
13
All la large bo boulders ar are alive Some root vegetables are large boulders Therefore some root vegetables are alive
14
Some ome peo peop ples' es' ho homes mes are are giant mansi ansio ons All giant mansions are houses Therefore some houses are peoples’ homes
15
Some ome re real ale ale do does no not co contai tain any any liquid quid All real ale is water Therefore some water does not contain any liquid
16
All ve vehicles on on th the ro road ar are bu buses Some vehicles on the road are not cars Therefore no cars are buses
17
All sa sailboats are bu buoyant in in wa water ter Some house bricks are buoyant in water Therefore some house bricks are sailboats
18
Some old men work as fishermen No young girls are old men Therefore no young girls work as fishermen
19
All mountain goats are mammals No mammals are invertebrates Therefore some invertebrates are mountain goats
20
No na naughty ghty chil hildren ren do do we well in sc schoo hool All those who do well in school are well behaved Therefore some of those who are well behaved are not naughty children
END ANSWERS TO FOLLOW…
Explanation: Syllogisms are most easy to get right when logical necessity agrees with common sense. For example number 12: No shiny red apples contain deadly poison Some types of fruit contain deadly poison Therefore some types of fruit are not shiny red apples The conclusion follows logically from the premises and also is believable; we know from experience that not all fruit are apples, so there is no conflict between our ‘heuristic reasoning’ based on past experience and our ‘analytical reasoning’ working working out the answer from the premises. However taking another example number 3: Some computers are not laptops Some laptops are not MacBooks Therefore some computers are MacBooks The conclusion is believable; we know from experience that MacBooks are indeed a type of computer BUT this does conclusion does not follow logically logically from the premises so is invalid. In this case our heuristic reasoning is in conflict with our analytical reasoning and we will find it a lot harder to get t he answer right. When these two modes of mental processing are in conflict and we inappropriately inappropriately use our heuristic reasoning it is called belief bias. bias . I have listed below for each syllogism whether the conclusion was valid or invalid, believable believable or unbelievable unbelievable and have marked a 1 next to the syllogisms where the belief bias effect was likely to occur. Answers:
