Sabres Quick Guide to Logic

[Sabre]

A quick guide to logic

We all use logic, even if you don't realise. When you lose your keys, what do you do?

You don't see a pyschic.

You don't claim the goverment took them and are covering the truth.

You don't claim that you have the keys, but you need more grant money to produce them.

Instead, you look for them in places where they would likely be until you find them. That is logic.

The next thing about logic is the ability to take a moment to seperate the fact from opinion. Facts are objective, which means they can be messured. How many fingers you have is a fact. Opinions cannot be messured. Chocolate being the best ice cream is an opinion. Backing up opinion with fact is good.

Red Herrings give the impression of being related, but aren't, and are thus irrelevent.

A key compenent of logic is to admit when your wrong or admit when someone has a good point, even if you disagree. If you look in your left pocket for the keys, you don't claim you have found the keys and leave the house to save face.

[DZComposer]

P -> Q

P

--------

Q

Bitches don't know 'bout my Modus Ponens.

But wait! A challenger appears!

P -> Q

Q

---------

P

FAIL! Affirming the consequent is a fallacy.

EDIT: For those that don't know, the first one reads in English: "If P, then Q. P, therefore Q." The second one reads "If P, then Q. Q, therefore P."

On a more serious note, a rundown of the common informal fallacies is in order.

1. The Straw Man. This is responding as if your opponent said something different that is easier to attack.

Example:

Person A: Furry conventions draw people into a town that will spend money.

Person B: Furry Conventions are bad. Beastiality should not be encouraged.  <- Straw Man Argument. Person A said nothing about beastiality.

2. The Slippery Slope. This is saying that your opponents position will reach some conclusion down the road without backing it up.

Example: Gun control is wrong! First, they'll take the RPGs. Then, they'll take the machine guns. Then, the assault rifles. And before long, you won't be able to own a gun at all. <- No evidence is given for any of the claims. I'm sure you've heard this one before. This is one of the most common examples of a slippery slope out there.

3. Reductio ad Hitlerum, or Godwin's Law. This is the claim that something has some connection to Hitler, Nazis, or The Holocaust so it must be bad.

Person A: I love my VW Beetle.

Person B: Beetles suck. Know why? Hitler had them made. <- Just because Hitler commissioned Ferdinand Porsche to design the VW Beetle doesn't diminish the effectiveness of Porsche's design.

4. Equivocation. Mixed up word meanings.

Example: Pain isn't generic. Muscle tension causes headaches and degraded cartilage causes arthritis pain. Since pain isn't generic, your pain reliever shouldn't be either. Choose Tylenol instead of store brands (this is paraphrasing an actual Tylenol radio ad). <- Generic drugs are drugs not made by the initial manufacturer. Tylenol is the brandname. Store-brand acetaminophen is a generic. But, the ad starts using a different meaning of generic: Not specific. Last I checked, Tylenol was a medication for "generic pain"....

5. False Dilemma. Give your opponent an incomplete set of options and frame it as if it is a complete set of options.

Example: Either you support waterboarding, or you support terrorism. <- You can be anti-terrorism and anti-waterboarding.

6. Two Wrongs. Two wrongs do not make a right in action. Neither do they in logic.

Example:  Furries should not protest child pornography because their pornography is at least as offensive, if not more. <- And this debunks a furry protesting child porn how? Notice how no attempt is made to counter the argument.

7. Unwarranted Generalization. Making a generalization without sufficient evidence to back it up.

Example: I've seen two Krystal fans that talk about having sex with her. All Krystal fans must be perverts. <- As we all know, not all Krystal fans are perverts.

8. Ad Hominem. Instead of attacking the argument, attack the person.

Example:

Person A: Heavy is an effective class. He excels at area denial, especially when paired with a medic or near a dispenser.

Person B: Of course you would say that. All you do is camp the dispenser. Stupid camper. <- Instead of arguing the weaknesses of playing heavy, person B attack's A's playing style.

9. Appeal to Ignorance. Arguing that it's true because you can't disprove it.

Example: There is no evidence that Andross didn't push Krystal, so he must have.

10. Begging the Question. The premise of the argument assumes the conclusion to be true.

Example: Star Fox needs to return to rail shooting in order to revitalize. This is because rail shooting has been the vital force of the series. <- Notice how circular this is?

[Asper Sarnoff]

This should really be obligatory to read and understand before anyone is allowed to roam freely around the internet.

[Mr. Krystal]

Actually Sabre, opinions can be facts IF quantifiable. For example, "It is my opinion that the sun will rise tomorrow." Tomorrow, when the sun rises, my opinion will be fact, even though it remains an opinion. That's because I used quantifiable terms. If I said, "It is my opinion that tomorrow will be better than today." that statement is not universally quantifiable, and will never be labeled factual by all.

An interesting logic that I was aware of for a long time, but didn't know was formally measured until days ago:

Self-Stultifying Arguments

Arguments that cannot be logically made. They "fall over themselves" simply by their own existence.

Primary Example:

"This statement is false." - If the quoted statement is true, then it is false. If it is false, it remains false.

You wouldn't think people would make such stupid arguments, but they come in all kinds of subtle forms, such as:

Famous Examples:

"There is no truth." - I don't believe what you just said, by your own logic.

"All truth is relative." - So, is that statement only true for you?

"Nothing can be known for certain." - Not even this?

"All generalizations are false." - ...is a generalization.

"Words never describe reality, only one's interpretation of it." - Then how can you make a statement about words if it's only your interpretation?

"Truth only comes after verification." - Who verified this statement? How would you test it?

"All worldviews/religions are true." - Even the ones claiming that all others are not true?

"God is indescribable." - "Indescribable" is a description.

"The past cannot be known." - Including the beginning of the sentence you were in the process of writing?

This concept, while appearing silly, is actually quite important, because it implies absolute truths through the inability to even successfully state a counter-argument, let alone defend it. My favorite, which I have stated many times:

"There is no absolute truth." - Is that statement ALWAYS true?

[Sabre]

8. Ad Hominem. Instead of attacking the argument, attack the person.

Example:

Person A: Heavy is an effective class. He excels at area denial, especially when paired with a medic or near a dispenser.

Person B: Of course you would say that. All you do is camp the dispenser. Stupid camper. <- Instead of arguing the weaknesses of playing heavy, person B attack's A's playing style.

A better example of that is "You can't trust person As opinion on cars because he was once arrested for assault."

The WRONG appeal to athority.

Citing an opinion of an expert can be relevent especially in casual logic.

So asking an abortion doctors opinion on the science of abortion makes sence (does it feel pain ect) is fine.

However, just because they are in a related feild does not mean their opinion is valid.

So asking if abortion is right is NOT the Dr area of expertise and should be ignored.

The most famous example of this is from an american TV ad which states

"I'm not a dr, but I play one on TV" then give health advice.

[DZComposer]

I left out a big one that is quite prominent in US politics right now.

Appeal to Fear - A sub-fallacy of appeal to emotion, this is an attempt to discredit your opponent by suggesting that there is something frightening about the opponent's position.

Example: If Obama passes healthcare, we will be one step closer to a communist dictatorship! <- Instead of attacking the weaknesses of the legislation, the argument tries to sow fear of the legislation by presenting it as a path towards a Stalinist state.

A better example of that is "You can't trust person As opinion on cars because he was once arrested for assault."

I agree that there is an element of ad hominem in there, but this one also contains a plain-obvious red herring. I would say the red herring sticks out more, as the assault has nothing to do with cars.

A classic ad hominem example is this:

Person A: Marijuana should be legalized. It is not addictive, and impairs you less than alcohol.

Person B: You smoke pot every day. You can't trust a pothead's views on drug issues.

Or the obvious:

Person A: The federal reserve's policies have caused serious strain on our financial system, and played a major role in the recent crash. We should go back to the gold standard.

Person B: You're an idiot.

The WRONG appeal to athority.

Citing an opinion of an expert can be relevent especially in casual logic.

So asking an abortion doctors opinion on the science of abortion makes sence (does it feel pain ect) is fine.

However, just because they are in a related feild does not mean their opinion is valid.

So asking if abortion is right is NOT the Dr area of expertise and should be ignored.

The most famous example of this is from an american TV ad which states

"I'm not a dr, but I play one on TV" then give health advice.

Allow me to clean this up a bit.

I learned this as the Irrelevant Authority Fallacy, which is defined as citing a source that has no authority on the issue.

Example: John is a PhD candidate in Astrophysics, and he says that the reason banks are failing is because they put too much money into bonds. <- Banking has nothing to do with Astrophysics. John is no authority on banking.

This one came up recently when a femanist claimed all games are sexist and evil because she saw pictures of a few and can say they are sexist. This is both faulse generization AND wrong appeal to athority.

I don't see the irrelevant authority here. It just seems like a classic Unwarranted Generalization to me.

Once you learn fallacies, you can have loads of fun. Let's look at the New York Times Opinion Page, shall we?

Once partisan reconciliation is used for this bill' date=' it will be used for everything, now and forever. The Senate will be the House. The remnants of person-to-person relationships, with their sympathy and sentiment, will be snuffed out. We will live amid the relationships of group versus group, party versus party, inhumanity versus inhumanity.

http://www.nytimes.com/2010/03/16/opinion/16brooks.html?ref=opinion

[/quote']

A classic Slippery Slope, with a touch of appeal to fear.

Of course you'll find them in the opinion page, but you'll see them pop up everywhere. You'll notice characters in TV shows use them. They'll pop up in ads, like the obvious equivocation in the Tylenol ad I mentioned earlier.

I wish I had time to get more, but I have to leave.

[Sabre]

Your right, I'll change that.

The assault example still stands as it's implying something negative about his character (he was once arrested) not the issue.

[DZComposer]

I don't disagree that there is ad hominem in that example. I just think that the stronger fallacy is the red herring.

[Guest Julius Quasar]

A quick guide to logic

We all use logic, even if you don't realise. When you lose your keys, what do you do?

You don't see a pyschic.

You don't claim the goverment took them and are covering the truth.

You don't claim that you have the keys, but you need more grant money to produce them.

Instead, you look for them in places where they would likely be until you find them. That is logic.

The next thing about logic is the ability to take a moment to seperate the fact from opinion. Facts are objective, which means they can be messured. How many fingers you have is a fact. Opinions cannot be messured. Chocolate being the best ice cream is an opinion. Backing up opinion with fact is good.

Red Herrings give the impression of being related, but aren't, and are thus irrelevent.

A key compenent of logic is to admit when your wrong or admit when someone has a good point, even if you disagree. If you look in your left pocket for the keys, you don't claim you have found the keys and leave the house to save face.

I agree.  As an up-and-coming Real Estate Appraiser, I know I...we, me and my colleagues, have to use logic, and fact when when determining the value of real estate.  Not opinions.  Facts, like comparable sales, sales histories of the subject property, and the properties in the neighborhood similar in characteristics to the subject property. We also determine whether the subject property is at its highest and best use (square footage, number of bedrooms, potential for add on or not, potential for parcel/land subdivision or not, etc.).

We gotta use data, facts, statistics, things like that.  We can't let things like "Oh, the subject property is haunted, that could impact value" influence our work...why?  Because "haunted" is more of an opinion, not officially proven a fact.  It's like...superstition.

[ThePointingMan]

P -> Q

P

--------

Q

Bitches don't know 'bout my Modus Ponens.

But wait! A challenger appears!

P -> Q

Q

---------

P

FAIL! Affirming the consequent is a fallacy.

EDIT: For those that don't know, the first one reads in English: "If P, then Q. P, therefore Q." The second one reads "If P, then Q. Q, therefore P."

So... I know what P->Q P is in English, but what does "If P, then Q. P, therefore Q." The second one reads "If P, then Q. Q, therefore P." mean. Of topic, but something that's been bugging me for a looong time.

On a side note, I'd fail miserably at appraising .

[DZComposer]

P and Q are variables. As are any other letters.

Operators:

-> means a conditional, or"if" statement. This may also be shown as ?. (P ? Q)

! means not. Could also be ~ or ¬.

* means and (also /).  And is true is both conditions are met.

| is nand. Nand means "not and." It is true so long as both conditions are not true, IE the opposite of and.

/ means or. Or is true if one or both conditions are met.

? means xor. Xor means exclusive or, which means one or the other but not both.

= means equal, but usually it is a triple bar (?).

Anything in parenthesis means evaluate it before evaluating external operators (just like in math).

Back to Modus Ponens:

P is the antecedent, or "premise". Q is the consequent of the premise.

Perhaps it would help if I assigned values to the variables.

P = It is raining outside

Q =  I will get wet

P -> Q

P

--------

Q

becomes

It Is Raining Outside -> I will Get Wet

It is raining outside

------------------------------------------------

I will get wet

Which becomes

If it is raining outside, then I will get wet. It is raining outside, therefore I will get wet.

Modus ponens is one of the most basic arguments. If you combine two of them, you get a Hypothetical Syllogism:

P -> Q

Q -> R

---------

P -> R

(If P then Q. If Q then R. Therefore, If P then R.)

There is also the reverse of Modus Ponens, called Modus Tollens.

P -> Q

!Q

--------

!P

(If P then Q. Not Q, therefore not P.)

If I assign the values I did earlier, this would look like this:

If it is raining outside, I will get wet.

I did not get wet.

Therefore, it is not raining outside.

You can also add different operators to it:

(P / Q) ->  R

P * Q

----------------

R

(If P or Q, then R. P and Q. Therefore, R.)

Mind the or. This would change if we used XOR instead:

(P ? Q) ->  R

P * Q

----------------

R

(If P or Q exclusively, then R. P and Q. Therefore, R.)

This argument is invalid. P ? Q means P or Q but not both.

Given these premises, the only conclusion that can be validly reached is !R (not R):

(P ? Q) ->  R

P * Q

----------------

!R

This brings up the difference between a valid argument and a sound argument.

A valid argument simple means an argument that is free of fallacies. It can be wrong, but valid.

A sound argument is both valid and true.

Consider this argument:

If a man has sex, he will get pregnant.

A man has sex.

Therefore, he will get pregnant.

It's a valid modus ponens argument (P = a man has sex, Q = he will get pregnant) but, but the consequent, and thus the conclusion, are preposterous. It is not sound.

[ThePointingMan]

Ok, I get the statement now. In the game BlazBlue, Arakune's special attacks are Zero vector, if P then Q, Y.two-dash, equals zero, F of G, and F-inverse, and I was wandering why, it still doesn't quite make sense for the attacks to be named those, but I see they are all related to that statement. Also I've never seen an if statement using ->.

Other then this, I don't think I have much to add to the actual topic here.

[DZComposer]

They're jokes on math and logic, which are the fundamentals of programming! Is the character a programmer or mathematician by chance?

A Zero Vector is an algebraic vector with no direction.

If P then Q is a conditional statement.

Not sure what y.2- is

= 0 is obvious.

f(g) (F of G) means "Function of G" in math. The function name "g" may have a special meaning in this case, but I am not aware of it.

f-inverse means inverse function.

[ThePointingMan]

That's him:)

He's not specifically a mathematician, but he is always looking to gain knowledge, reading books of all sort.

[Sabre]

I don't disagree that there is ad hominem in that example. I just think that the stronger fallacy is the red herring.

It's still claiming that his argument is invallid because of a precieved negative trait. Attacking the person, not the argument.

One of my favourite falacies is Corilation = causation. I'm sure it was mentioned here already, but I couldn't find it. Anyway.

Most people have black hair

Most people eat rice.

Therefore rice gives you black hair.

This is also done by lumping together figures to make things soudn big.

60% of people have black hair

50% of people have blue eyes

110% of people have black hair or blue eyes. <-- This is more a statistics jumble then a logic one, but it still counts imo.

[CrypticQuery]

Aside with agreeing with most of the things said already, I can add one more thing to the conversation,

"MY BRAIN HURTS!" 

To be serious though, this is one deep conversation!

[DZComposer]

Basic logic is not difficult, and as an important thing to understand.

I did use some symbols and variables, but the reason I did is that it reduces things down to a pure logical form without the fluff of a statement.

Here are all the arguments I mentioned in English.

For instance, this is a modus ponens argument:

If you switch the 8 switches on MacBeth, you will go to Area 6.

You switch the 8 switches, thus you will go to Area 6.

Modus Tollens:

If you switch the 8 switches on MacBeth, you will go to Area 6.

You did not go to Area 6, thus you did not switch the 8 switches.

Hypothetical Syllogism:

If you switch the 8 switches on MacBeth, you will go to Area 6.

If you go to Area 6, you will go to Venom 2.

Therefore, if you switch the 8 switches on MacBeth, you will go to Venom 2

Conditional Or:

If you open the door or open a window, then you will let the rain in.

You open the door AND a window.

Therefore, you will let the rain in.

Conditional Xor:

If you push the green button or the red button, but not both, the door will open.

You push both the red and green buttons, therefore the door will NOT open.

It is not so important that you know the names, but rather that you recognize the validity of them. If you step back for a minute, you should realize that these arguments I listed here are common sense.

The fallacies can be harder to recognize, but once you learn them, you can spot them and reduce the number of fallacies you commit yourself.