Midterm

The midterm will be held at the beginning of class on Thursday, October 25th. It's worth 15% of your overall grade, and will cover everything we've done in class so far:

• definitions of 'logic,' 'reasoning,' and 'argument'
• evaluating arguments (Chapter 6)
• types of arguments:
  -deductive (aim for certainty, are valid/invalid and sound/unsound) (Chapter 8)
  -inductive (generalizing from examples, are evaluated based how large and representative the examples in the premises are) (Chapter 7)
  -args by analogy (evaluated in terms of how similar the things compared are, and how relevant the similarities are to the conclusion being drawn) (Chapter 7)
  -args about cause/effect (correlation vs. causation) (Chapter 7)
  -abductive (inferences to the best explanation, evaluated in terms of coherence with background theories, simplicity, predictive power, falsifiability, etc.) (Chapter 12)
• the 10 or 11 fallacies covered in class so far (Chapter 5)

Get to studying!

Quiz You Once, Shame on Me

The first quiz will be held at the beginning of class on Thursday, September 27th. You will have about 25 minutes to take it.

There will be a multiple choice section, a section on understanding arguments, a section on evaluating deductive arguments, and a section where you provide examples of specific kinds of arguments. Basically, it will look like a mix of the homework, extra credit, and group work we've done in class so far.

The quiz is on what we have discussed in class from chapters 6, 8, and part of 7 of the textbook. Specifically, here's a lot of the stuff we've talked about in class so far that I expect you to know for the quiz:

• definitions of: logic, reasoning, argument, support, sound, valid, deductive, inductive
• understanding arguments
• evaluating arguments (truth and support!)
• deductive args (valid & sound)
• inductive args (there will only be a little on this, based on Tuesday's class)

The quiz is worth 7.5% of your overall grade.

Homework #1: Deductive Arguments

Homework assignment #1 is due at the beginning of class on Thursday, September 20th.  It's worth 3% of your overall grade.  The assignment is to complete the worksheet I hand out in class.

If you don'tt get it in class, you can download the worksheet here. Or, if you can't download it, here are the questions on the worksheet:

DIRECTIONS: Provide original examples of the following types of arguments (in premise/conclusion form), if possible. If it is not possible, explain why.

1. A valid deductive argument with one false premise.

2. An invalid deductive argument with all true premises.

3. An unsound deductive argument that is valid.

4. A sound deductive argument that is invalid.


MULTIPLE CHOICE: Circle the correct response. Only one answer choice is correct.

5. If a deductive argument is unsound, then:
a) it must be valid.
b) it must be invalid.
c) it could be valid or invalid.

6. If a deductive argument is unsound, then:
a) at least one premise must be false.
b) all the premises must be false.
c) all the premises must be true.
d) not enough info to determine.

7. If a deductive argument is unsound, then:
a) its conclusion must be false.
b) its conclusion must be true.
c) its conclusion could be true or false.

8. If a deductive argument’s conclusion is true:
a) then the argument must be valid.
b) then the argument must be invalid.
c) then the argument could be valid or invalid.

9. If a deductive argument is sound, then:
a) it must be valid.
b) it must be invalid.
c) it could be valid or invalid.

10. If a deductive argument is sound, then:
a) at least one premise must be false.
b) all the premises must be false.
c) all the premises must be true.
d) not enough info to determine.

11. If a deductive argument is sound, then:
a) its conclusion must be true.
b) its conclusion must be false.
c) its conclusion could be true or false.

12. If a deductive argument’s conclusion is false:
a) then the argument must be valid.
b) then the argument must be invalid.
c) then the argument could be valid or invalid.

Evaluating Deductive Arguments Handout

Here are the answers to the handout on evaluating deductive arguments that we did as group work in class.

1) All bats are mammals.
All mamammals live on earth.
All bats live on earth.

P1- true
P2- true
support- valid
overall- sound

2) All email forwards are annoying.
Some email forwards are false.
Some annoying things are false.

P1- questionable ("annoying" is subjective)
P2- true
support- 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)

3) All males in this class are humans.
All females in this class are humans.
All males in this class are females.

P1- true
P2- true
support- invalid (the premises only tell us that males and females both belong to the humans group; we don't know enough about the relationship between males and females from this)
overall- unsound (bad support)

4) No humans are amphibians.
All frogs are amphibians.
No frogs are humans.

P1- true
P2- true
support-  valid (the premises say that frogs belong to a group that humans can't belong to, so it follows that no frogs are humans)
overall- sound

5) All bats are mammals.
All bats have wings.
All mammals have wings.

P1- true
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)
support- 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 support)

6) Some dads have beards.
All bearded people are mean.
Some dads are mean.

P1- true
P2- questionable ("mean" is subjective)
support- 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)

7) Oprah Winfrey is a person.
Some people ate tacos yesterday.
Oprah Winfrey ate tacos yesterday.

P1- true
P2- true (you might not have directly seen anyone eat tacos, but you have a lot of indirect evidence... with all the Taco Bells, Don Pablos, etc., surely lots of people ate tacos yesterday)
support- invalid (the 2nd premise only says some ate tacos; Oprah could be one of the  people who didn't)
overall- unsound (bad support)

8) All students in here are mammals.
All humans are mammals.
All students in here are humans.

P1- true
P2- true
support- 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.

P1- true!
P2- true
P3- questionable ("scary" is subjective)
support- valid (same structure as in argument #1, just with an extra premise)
overall- unsound (bad 3rd premise)

10) If Sean sings, then students cringe.
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)
P2- false
support- valid
overall- unsound (bad premises)

11) If Sean sings, then students cringe.
Sean isn't singing right now.
Students aren't cringing right now.

P1- questionable (again, you don't know)
P2- true
support- 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)

12) All students in here are humans.
Most humans are shorter than 7 feet tall.
Most students in here are shorter than 7 feet tall. 

P1- true
P2- true!
support- invalid (the premises state a strong statistical generalization over a large population, and the conclusion claims that this generalization holds for a much smaller portion of that population; even though it's likely that most students in here are, in fact, shorter than 7 feet tall, it nevertheless could be true that the humans in here are a statistical anomaly)
overall- unsound (bad support)

13) (from Stephen Colbert)
Bush was either a great prez or the greatest prez.
Bush wasn’t the greatest prez.
Bush was a great prez.

P1- questionable ("great" is subjective)
P2- questionable ("great" is subjective)
support- valid (it's either A or B; it's not A; so it's B)
overall- unsound (bad premises)

14) If Sean sings, then students cringe.
Students are cringing right now.
Sean is singing right now.

P1- questionable (again, you don't know)
P2- false
support- 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)

15) If Sean sings, then students cringe.
Students aren't cringing right now.
Sean isn't singing right now. 

P1- questionable (again, you don't know)
P2- true
support- valid 
overall- unsound (bad 1st premise)

16) If there is no God, then life is meaningless.
Life isn't meaningless.
There is a God.

P1- questionable (that's not an obvious claim to prove or disprove)
P2- questionable (again, that's not an obvious claim to prove or disprove)
support- valid (the same structure as argument #15)
overall- unsound (bad premises)