LESSON 7: Logic

8/18/2019 LESSON 7: Logic

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Evaluating ArgumentsIn evaluating arguments, 2 aspects are considered:1) Truth of the Premises (Content)2) Validity of easoning (!orm)

The actual content of the premises ("hether the content is factually true or not is not theconcern of logic #ut of epistemology)

Thus, "hen "e claim a syllogism to #e T$%, "e are not &uestioning "hether the premisesare in fact true #ut if the premises "ere true'

In order to properly evaluate an argument "e need to as ourselves 2 &uestions'1) re the premises true*2) +oes the conclusion follo" from the premise*

If the premises are true-factually correct

If the conclusion follo"s from the premisesvalid

If the syllogism is factually correct and valid sound

Note: the argument subjected to logical evaluation is called CATEGORICAL SLLOGIS!"

%lements:1) .tandard !orm: /a0or Premise

/inor Premise Ideal !orm Conclusion

ther Possi#le !orms1) m / C2) C / m3) / C m

2) Parts 4 #asic unit is called a T%/

In a standard form syllogism, there can only #e a ma5imum of 6 terms- 2 for eachpropositions'

1) The su#0ect term of the conclusions is the minor term (.)' The predicate of theconclusion is the major term (P), the term that appears in #oth premises #ut notin the conclusion is the middle term (/)'

2) The premise that contains the ma0or term is the ma0or premise (usually a generafact)- the premise containing the minor term is the minor premise (usually aparticular fact)

7ints:1) 8either the &uanti9er and copula is considered in the conclusion, rather, it is

only used to determine the type of statement'2) +etermine the su#0ect term and predicate term of the conclusion, then

determine the ma0or and minor premise'


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Rules on validating categorical syllogisms It can #e divided into 2 parts- rules on terms and rules on propositions'

A) Rule on Terms

Rule 1: categorical syllogism must contain only 3 terms' %ach must appear t"ice#ut not on the same proposition and must have the same sense throughout the argument'

!allacies:1) !allacy of terms2) !allacy of %&uivocation3) !allacy of mphi#oly

ll candies are s"eet .ome girls are s"eet.ome girls are candies

Rule 2: The middle term must #e distri#uted in at least 1 premise'

ll pigs are mammalsll men are mammals ll men are pigs

1' !allacy of undistri#uted middle term

Rule 3: The middle term must not #e found in the conclusion'

ll the students are thomasians Pete is a student Pete is a thomasian student

1' !allacy of misplaced middle term

Rule 4: ny term distri#uted in the conclusion must #e distri#uted in the premises'

!allacy:1' !allacy of illicit ma0or term 4 this occurs "hen the ma0or term is

undistri#uted in the premise #ut is distri#uted in the conclusion'(;ut not vice versa)

2' !allacy of illicit minor term 4 this occurs "hen the minor term is

undistri#uted in the premise #ut is distri#uted in the conclusion'(;ut not vice versa)

Illustration 1Illustration 2 ll animals are organisms ctorsare models 8o insect is an animalctors are men


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Insects are not organisms /enare models

/ (+) P ($) / (+) P($) . (+) % / (+) / (+) .($) . (+) % P (+) . (+) P($)

B) Rules on Propositions

Rule 5: 8o standard form syllogism "ith 2 negative premises (%, ) is valid'

8o plants are humans8o !ilipinos are animals8o !ilipinos are humans

Note: There can be no conclusion

Rule 6: If #oth premises are a


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.ome men are la"yers .ome nurses are !@s .ome televisions aredigital .ome 9lipinos are men .ome 9lipinas are nurses .ome gadgets are nottelevisions.ome 9lipinos are la"yers ll 9lipinas are !@s .ome gadgets are notdigital

Venn +iagram

Proponent: Aohn VennPurpose: +etermines "hether a given categorical syllogism is a valid or invalid'Components:

Note: &niversals 'A( E) are shaded *articulars 'I( O) are


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/ethod1) +iagram the premises2) Chec "hether diagrams contains the content of the conclusion3) +etermine its validity

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LESSON 7: Logic