2 logic, validity, and truth

8/13/2019 2 Logic, Validity, And Truth

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Logicis the study of the methods andprinciples used to distinguish correct from

incorrect reasoning.

Logicis solely interested in the logicalnecessity (consequential relationship)existing between the conclusion and thepremises.


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is the

correspondence of a proposition or assertionto fact.

is when the conclusion isnecessarily inferred from the premises.


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YES NO

90 % 10 %

Do you believe that Mr. Reyes committeda crime of falsification of documents?

Mr. Reyes is guilty since 90% said hecommitted a crime.


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The vast majority of the

population believes that Mr. J is

guilty.

The majority could not be

possibly be wrong.

Therefore, Mr J. must be guilty.


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When interviewed by an American reporter,sometime in November, 1985, the formerFirst Lady, Imelda Marcos, said about herself:

If I am evil then why am I still good-looking?Surely if I was all the bad things they say of

me, it would show. I would not look like this ifI were corrupt. Some ugliness would settledown on my system.


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Since, being beautiful isequivalent to being morallygood.

Imelda Marcos is beautiful.

Therefore, Imelda Marcos ismorally good.


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The conclusionof an argument is the position orstand that a person takes regarding an issue.

Therefore, Mr. J must be guilty.

Conclusion-Indicators Therefore, thus, hence, so, accordingly, for

this reason, in consequence, consequently,proves that, as a result, follows from, whichshows that, which means that, it follows that,which points to the conclusion that


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Premisesare the supports or evidences givenfor the position that one takes regarding an

issue/ conclusion.

Premise-indicators

Because, as, follows from, as shown by,

inasmuch as, as indicated by, the reason

is that, for the reason that, in view of the

fact


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HELLO. DLSU is located in Taft Avenue.

Good Morning. The moon is made of cheese.

What time is it? Today is Monday.

Can you please get me aglass of water? Four plus three equals seven.

Get out of here! Cebu is the capital of the Philippines.

Oh no! Light travels at around 186, 000

miles per second.

Constatives are

statements that can be

either true or false.

These are statements

that are neither true

nor false.


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Deductionis reasoning from general to thespecific.

Inductionis reasoning from specific togeneral.

All men are mortal.

Socrates is a man.

Therefore, Socrates is mortal.


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All pigs are mammals.

All mammals are warm-blooded.

Therefore, all pigs are warm-blooded.

1. In every deductive argument, a claim ismade that if the premises are true, theconclusion cannot be false.

2. If the premises isvalid, the conclusionnecessarily follows from the premises.


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The swan that I saw last Mondaywas white.

The swan that I saw last Tuesday

was white. The swan that I saw last

Wednesday was white.

Therefore, all swans are white.

Therefore the next swan I see will

be white.


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In every inductive argument, even if all thepremises are true, the conclusion can only be

probably true.


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1. All cats are mammals. All mammals are warm-blooded.

Therefore, all cats are warm-blooded.

2. All men are mortal. Socrates is a man. Therefore, Socrates is mortal.


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3. All kittens are mammals. All cats are mammals.

Therefore, all kittens are cats.

4. All tigers are pigs. All pigs are snakes. Therefore, all tigers are snakes.


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1. the argument must be valid.

2. all its premises must be true.


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All Chinese are Asians. All Mandarins are Chinese.

Therefore, All Mandarins are Asians.


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All Mandarins are Germans. All Filipinos are Mandarins

Therefore, All Filipinos are Germans.


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All dogs have tails. All cats have tails.

Therefore, all cats are dogs.


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Pedro loves Juana. Therefore, Juana loves Pedro.


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Mr. Santos is a millionaire Therefore, he is not corrupt.

He does not steal the peoples money.

It may be true that Mr. Santos, being amillionaire, is not corrupt and is not stealingpeoples money. This is the good case of itmay be but it need not be.


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IDEAS JUDGMENT REASONING

TERM PROPOSITION INFERENCE

-from general to specific

All man is rational.Socrates is a manTherefore, Socrates is man.

-from specific to generalPlants die.Animals die.Men die.All of them are living beings.Therefore, all living beings die.


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4.Jhoan, Madel, Emmanor, and Lizza attended a birthday party.Each wore a white, blue, red, and yellow dress. The birthdaycelebrant received a chocolate, picture frame, bag, and stuff toyfrom above mentioned visitors. From the facts below, identify the

gifts each girl gave and the color of the dress they wore in theparty.

The one who gave the chocolate arrived together with Jhoan andLizza. The girl wearing a white dress sat beside Emmanor. Thecelebrant received the stuff toy from the girl wearing the yellow

dress. Lizza, who gave the bag, wore her favorite blue dress. Thegirl wearing the red dress did not give the chocolate. The girl whogave the stuff toy did not know Emmanor.


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5.Kate has finished covering her books for this semester. Her books arePhysics, Computer, Logic, and Mathematics. Each of her book wascovered with one particular color: pink, cream, lavender, and maroon.The book in her most difficult subject was covered pink. None of herbook was covered with the same first letter of the subject and first letterof its covers color. Physics and the maroon books were the very first twobooks she covered. Computer book was covered in lavender. What is themost difficult subject for Kate?

PINK CREAM LAVENDER MAROON

PHYSICS

COMPUTER

LOGIC

MATHEMATICS

2 logic, validity, and truth

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