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Lesson 21. Laws of detachment and syllogism. Deductive reasoning. Deductive reasoning is the process of using logic to draw conclusions from given facts, definitions, and properties. When 2 related statements are true, deductive reasoning can be used to make a conclusion Foe example:

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Lesson 21

Lesson 21

Laws of detachment and syllogism


Deductive reasoning
Deductive reasoning

  • Deductive reasoning is the process of using logic to draw conclusions from given facts, definitions, and properties



Using deductive reasoning
Using deductive reasoning be used to make a

  • All of Martha’s children have blue eyes. Blaine is Martha’s son.

  • Therefore______________________________

  • Simone wears blue and red on game days. Today is game day.

  • Therefore ___________________________________

  • To check out a book from the library, you must have a library card. Alex checked out a book from the library.

  • Therefore ___________________________________


Law of detachment
Law of detachment be used to make a

  • For 2 statements p and q,

  • when “ if p, then q” is a true statement and p is true, then q is true

  • We use the Law of Detachment to draw valid concluding statements.

  • When the given facts are true, then correct logic can lead to a valid conclusion


Caution
caution be used to make a

  • Be sure to draw conclusions that are based on the information given. Do not make assumptions that are not logically sound or which have not been stated in the question


Using the law of detachment
Using the law of detachment be used to make a

  • When it is cold outside I wear my warm jacket. It is cold outside today.

  • Therefore_____________________________

  • If an angle is acute, then it cannot be obtuse.. Angle D is acute.

  • Therefore ________________________________

  • I get paid every Friday. Today is Friday.

  • Therefore_____________________________


Law of syllogism
Law of syllogism be used to make a

  • When “If p , then q” and

  • If q , then r” are true statements, then “If p, then r” is a true statement



Using law of syllogism
Using law of syllogism be used to make a

  • If the wind blows from the North, then the temperature will drop. If the temperature drops, then Joe will need to wear a jacket.

  • Therefore if the wind blows from the North, then _______________

  • If I oversleep tomorrow morning, then I will miss my ride to school. If I miss my ride to school, then I will get a detention.

  • Therefore, if I oversleep tomorrow morning, then ________________


Drawing valid conclusions
Drawing valid conclusions be used to make a

  • Ten dimes are worth one dollar. One dollar is worth 100 cents.

  • Therefore ____________________________________

  • This is the Law of _____________________

  • A car requires an oil change every 3000 miles. Jane’s car has been driven 9000 miles since its last oil change.

  • Therefore ____________________________

  • This is the Law of ____________________________


Draw a valid conclusion and identify the law used
Draw a valid conclusion and identify the law used be used to make a

  • If Maria wants to see a movie, then she goes to the theater. If Maria goes to the theater, then she buys popcorn.

  • Conclusion:_______________

  • Law:_______________

  • If it is raining then I will take an umbrella. Today it is raining.

  • Conclusion:___________________________

  • Law:_____________________________________


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