1) All kangaroos are marsupials.
All marsupials are mammals.
All kangaroos are mammals.
P1- true2) (from Stephen Colbert)
P2- true
structure- valid
overall - sound
Bush was either a great prez or the greatest prez.
Bush wasn’t a great prez.
Bush was the greatest prez.
P1- questionable ("great" is subjective)3) Some people are funny.
P2- questionable ("great" is subjective)
structure- valid (it's either A or B; it's not A; so it's B)
overall- unsound (bad premises)
Sean is a person.
Sean is funny.
P1- true (we might disagree over who specifically is funny, but nearly all of us would agree that someone is funny)4) All email forwards are annoying.
P2- true
structure- invalid (the 1st premise only says some are funny; Sean could be one of the unfunny people)
overall- unsound (bad structure)
Some email forwards are false.
Some annoying things are false.
P1- questionable ("annoying" is subjective)5) All bats are mammals.
P2- true
structure- valid (the premises establish that some email forwards are both annoying and false; so some annoying things [those forwards] are false)
overall - unsound (bad first premise)
All bats have wings.
All mammals have wings.
P1- true6) Some dads have beards.
P2- true (if interpreted to mean "All bats are the sorts of creatures who have wings.") or false (if interpreted to mean "Each and every living bat has wings," since some bats are born without wings)
structure- invalid (we don't know anything about the relationship between mammals and winged creatures just from the fact that bats belong to each group)
overall- unsound (bad structure)
All bearded people are mean.
Some dads are mean.
P1- true7) This class is boring.
P2- questionable ("mean" is subjective)
structure- valid (if all the people with beards were mean, then the dads with beards would be mean, so some dads would be mean)
overall- unsound (bad 2nd premise)
All boring things are taught by Sean
This class is taught by Sean.
P1-questionable ("boring" is subjective)8) All students in here are mammals.
P2- false (nearly everyone would agree that there are some boring things not associated with Sean)
structure- valid
overall- unsound (bad premises)
All humans are mammals.
All students in here are humans.
P1- true
P2- true
structure- invalid (the premises only tell us that students and humans both belong to the mammals group; we don't know enough about the relationship between students and humans from this; for instance, what if a dog were a student in our class?)
overall- unsound (bad structure)
9) All hornets are wasps.
All wasps are insects.
All insects are scary.
All hornets are scary.
All humans are shorter than 10 feet tall.
All students in here are shorter than 10 feet tall.
Sean is singing right now.
Students are cringing right now.
Sean isn't singing right now.
Students aren't cringing right now.
Students aren't cringing right now.
Sean isn't singing right now.
Students are cringing right now.
Sean is singing right now.
All wasps are insects.
All insects are scary.
All hornets are scary.
P1- true!10) All students in here are humans.
P2- true
P3- questionable ("scary" is subjective)
structure- valid
overall- unsound (bad 3rd premise)
All humans are shorter than 10 feet tall.
All students in here are shorter than 10 feet tall.
P1- true11) If Sean sings, then students cringe.
P2- true!
structure- valid (same structure as arg #1)
overall- sound
Sean is singing right now.
Students are cringing right now.
P1- questionable (since you haven't heard me sing, you don't know whether it's true or false)12) If Sean sings, then students cringe.
P2- false
structure- valid
overall- unsound (bad premises)
Sean isn't singing right now.
Students aren't cringing right now.
P1- questionable (again, you don't know)13) If Sean sings, then students cringe.
P2- true
structure- invalid (from premise 1, we only know what happens when Sean is singing, not when he isn't singing; students could cringe for a different reason)
overall- unsound (bad 1st premise and structure)
Students aren't cringing right now.
Sean isn't singing right now.
P1- questionable (again, you don't know)14) If Sean sings, then students cringe.
P2- true
structure- valid
overall- unsound (bad 1st premise)
Students are cringing right now.
Sean is singing right now.
P1- questionable (again, you don't know)
P2- false
structure- invalid (from premise 1, we only know that Sean singing is one way to guarantee that students cringe; just because they're cringing doesn't mean Sean's the one who caused it; again, students could cringe for a different reason)
overall- unsound (bad premises and structure)
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For number 10, couldn't P2 be questionable b/c if we use the "Imagine a World" thing, we don't know anything about who the tallest person is?
ReplyDeletePlus, if we wanted to be assholes about it, you didn't say the tallest human "on earth" so you never know.
-Kirstin
The "Imagine-a-World" test is only used to test the argument's structure. When checking the premises, we care about reality, not imaginary scenarios.
ReplyDeleteSure, we might not know with absolute 100% certainty that the tallest human is under ten feet. (We don't even have to worry about intergalactic humans: perhaps there was some 11-foot-tall person wandering around in ancient times.) But it seems like a highly reasonable conclusion to draw.
I like to lower my standards to be reasonable. I don't need premises to be 100% indubitable to count them as good premises. I just need them to be highly likely to be true.