FAQs

Topic 1

Getting Started?

Q. Do you want us to read the Cafe chapter tutorials, do the tutorials and exercises first THEN listen to your moodle online lecture?

A. You can do it either way. Personally, I'd listen to the online lecture until it becomes unclear and I'd pause it. Then I'd turn to tutorial one of chapter one, work through the whole thing and then do the associated exercises 1.1a and 1.1b. (1.1c maybe too though that is Araucaria!). Then you could go back to the online lecture and/or just move to tutorial two. But remember: the best practice for the exams and Moodle quizzes (75% of your grade!) is to do the exercises.

Araucaria

Q. Where is all this Araucaria stuff?

A. You can best find it in the exercise 1.1c. You will see three parts to the directions about how to find and use Araucaria for this first posting. 1. Download the program. 2. Download the stuff specifically for our class. 3. A slide-show presentation for the directions.

 

Q. I'm trying to install and run Araucaria and its giving me an issue. I downloaded it and installed the program. When I try to run the program however I get this message, "could not find the main class program, will exit." I have no idea what this error means having never seen anything like it.

A. I think that the message sounds like you have an issue with Java, the program that runs Araucaria. Perhaps you didn't install the full 16mg download to get the latest version of Java?

My guess is that you should try the full (recommended) download again. If that fails, then you might have to tell me a bit more about your machine. And maybe we'll have to talk a bit about it......or it may be time to call the OU people on the help link: 248 370 4832.

 

Q. I can get Araucaria to work but the schemes don't work. Also, how do I get

I may need to get on WebEx with you to work out the kinks. But let me try this: First, go through the "slide--show" again, the one in exercise 1.1c, to see if there is something you miss with the schemes. You need to load them, then select the arrows, and finally choose the appropriate scheme. (It's so easy to miss something!)

Second, you can save a picture file of each argument individually. (Then you'll have to reply to yourself to post the last three!) Or you can finish one diagram for one argument, then restart the process for the second argument.

Homework to be turned in

Q. Just to make this clear and to feel assured, the only thing due this week for credit is the 1.1c homework?

This posting is the only thing from the Logic Cafe exercises that is for credit. BUT there is also the Cafe Check (did you find the Key Phrase? if not come to WebEx and I'll give it away...or see the RECORDED session where it is given away).

You'll also want to do the Online Lecture. And reply to someone else.

Still, none of these things have a deadline. And the important thing is to do all this work to prepare for Moodle Quizzes (20% of the grade total) and the two exams (55% of the grade total).

Inferences: DS, MP and MT

Q. Just for clarification, because I keep confusing myself, can you define MT, MP and DS? 

A. Sure. (But keep in mind that this is the subject of chapter 1...you should probably review that too.) Let me explain by example.

MT: If there is fire on the moon, then there must be oxygen there. But there is no oxygen. So there's no fire on the moon. If F then O. But no O, so no F.

MP: If there is fire in my laboratory enclosure, then there must be oxygen in it. There is fire! So, there must be oxygen in it (seeped in I suppose!)    If F then O. F, so O.

DS: There is oxygen or nitrogen in my laboratory enclosure. There is no oxygen it there. So, there must be nitrogen.  O or N, but not-O. So, N.

Identifying Arugments, exercises 1.2d, 1.2e

Q. I'm a little bit unsure what the difference is between nonargument (report) and nonargument (explanation). Is there a way to differentiate the two? Also, I'm confused as to what nonargument (illusion) is and how to recognize that

A. Reports just state the facts. But explanation tells us the cause or reason why something is so. So, it adds a bit more. (Careful to distinguish arguments from explanations...they both give reasons but arguments are different still because they give evidence to make you believe in something.)

One more thing: it's "illustration" meaning "example".

Q. Spell out just what those non-arguments are about, can you?

A First arguments try to convince. Reasons (premises) for a conclusion. These are of most interest to us in logic: reasoning! But other passages can be confused with arguments.

  1. Explanations: don't try to convince us of something, say that the sun shines (we know that!) but try to tell us why the sun shines: it emits lots of energy due to nuclear fusion.
  2. Reports: Don't try to convince or explain but just tell us the facts. (A long description that merely describes is a kind of report.)
  3. Illustrations: Don't try to convince or explain but give an example to "illustrate" what's going on.

Cafe checks

Q. What's up with the Cafe checks and where will I find the key phrases?

A.
key phrase

 

Topic 2

Validity and the (Hard) Sanchez example

Q. I guess I am a little confused about the two arguments. Sanchez stays at her banking job only if she gets a raise. So, if she gets a raise, she'll continue at the bank.  If there is a problem with the Sanchez argument why?

A. Think of an analogous case:

I pass this class only if I study.
I study.
So, I’ll pass the class.

This is too fast: The premises may be true but the conclusion could still fail. One might study but study the wrong things. Or one might study very hard but have a catastrophic final exam for some other reason.

Notice the difference between premise one as stated and “I pass this class if I study”. This gives more of a guarantee.

Now, think about:

There is fire only if oxygen is present.
There is oxygen present.
So, there is fire.

SAME FORM, SAME PROBLEM. The premises are true but the conclusion is NOT. Now, try to think about what is going on. (Idea: the premises do not guarantee that the conclusion is true in these invalid arguments.)

Q. An argument is valid just in case it is not possible that its conclusion be false while its premises are all true. SO: it must have true premises and true conclusion to be valid.?????

An argument is sound if and only if it is both valid and has only true premises. So what's the difference?

A. The answer to your first question is "no, a valid argument does not need to have true premises". Validity is a matter of form and not of what is in fact true.

Here's another example that may help:

All philosophers are spinners.
Halpin is a philosopher.
So, Halpin is a spinner.

This one is validates what on earth is a spinner? I don't know. The idea, though, is that IF we find out that this premise is true (or made true by giving 'spinner' a meaning), THEN the conclusion would have to be true.

So, actual truth has nothing to do with validity. Instead, being valid is having the right form to ensure the conclusion must be true if we (somehow) find that the premises are true.

A sound argument is like this but does in fact have true premises. Sound = Valid (right form) + true premises.

Gold Material

Q. How do we get credit for completing the gold exercises?

Good question. Gold material is for people who are working for a 4.0 or so. The only way I grade this is on the two exams. So, if you can do the work of this optional Gold stuff, please do. It won't ever hurt but it's beyond the call of duty. And it's not extra credit but only good for people who are getting an A anyway.

 

Topic 4

Q. How do I distinguish "neither" from "not both"?

A. a) Chris doesn’t get both an ‘A’ and a ‘B’.

This means that Chris might get one of the two grades. Still, Chris can’t get both: It’s not true that she gets both and ‘A’ and a ‘B’. Thus, this is the negation of both: ~(A&B). Another way to put the same thing is the logically equivalent: she either doesn’t get an ‘A’ or she doesn’t get a ‘B’ (because she doesn’t get both). Hence: ~Av~B. These two symbolizations are logically equivalent. You can do a truth table to see why.

b) Chris gets neither an ‘A’ nor a ‘B’.

This means that Chris definitely doesn’t get an ‘A’ and doesn’t get a ‘B’: ~A&~B. But, likewise, it the negation of either: She does not get either an ‘A’ or a ‘B’. ~(AvB).

 

Topic 6

Reviewing some of the exercises in 4.5c - I got confused over this
"If both Bates and Connors are politicians, Ames is disreputable" my response was D>(B&C) - but the answer is in reverse (B&C)>D - why? - to me they would seem both correct. Am I missing a process here?

The reason (B&C)>D is correct is that ‘B&C’ is the “If” clause of the English: "If both Bates and Connors are politicians, Ames is disreputable". This “if” clause always goes in the antecedent.

Also, notice that one can’t just switch around a horseshoe. For example, it means something different to say “if there is fire then there is oxygen” (always true) from “If there is oxygen, then there is fire” (usually false).

Q. How do I understand double negation?

A. First, if 'B' stands for "Bush is president" (true) then '~B' stands for "Bush is NOT president" (false). Then you could read '~~B' as "It's FALSE that Bush is NOT president"...true! because it is false to say he's not president.

Do the truth tables the same way. If 'B' is assigned True then '~B' is the opposite, False, hence '~~B' is the opposite again: true.

 

 

Topic 11

Q. I was going through some derivations and am stumped on two of the problems:

1. Premise: ~(P=Q)
Premise: P

Conclusion: ~Q

A1. Line 3 should be the assumption of Q. Then you need to derive P=Q. How do you do this? Work a little strategy. Think about using EQ in the end. The easiest thing to do is use this form: P=Q <--> (P&Q)v(~P&~Q). Hint: you’ll need to do vI along the way within the subderivation.

2. Premise: (M>N)v(O>P)
Premise: ~N

Conclusion: (M&O)>P

A2: For 2, you’ll need Assume the negation of your goal. Then do IM and DM (much as you’have done before in easier problems). You’ll end up with M, O, and ~P sub-derived. Form M&~P you can use DN and DM and IM to derive ~(M>N). Then do DS.