Determine the type of reasoning used. (Inductive,Deductive or Invalid) 1. Cory knows that David is shorter than Jennifer.     Cory also knows he is taller than Jennifer.     Cory reasons he is taller than David. (I think this is Deductive) 2. Cory is told that when Jennifer gets her chores done, then she will usually go to the mall. He also knows that Jennifer usually gets her chores done by 5 p.m Cory reasons that Jennifer will usually go to the mall by 5pm. (I think this is inductive) 3. David plays video games if and only if he finishes his homework. David did not play video games on Wednesday. Therefore David did not finish his homework on Wednesday.    

Expert Answers

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These two avenues to logical conclusions differ in specific ways.  Deductive (de: from; ductive: drawn) gets to a conclusion by moving from known data to new data: inductive (in: toward; ductive: drawn) moves toward new data from known data.  Inductive reasoning is not mathematical; that is, the new data is implied but not proven from the old data.  Deductive reason is irrefutable; the simplest form is “All A is B; all B is C; therefore all A is C” (all kangaroos are marsupials: all marsupials are animals; therefore, all kangaroos are animals).  Inductive reasoning deals not with “therefore” but with “maybe”:  All marsupials live in Australia; koalas live in Australia; therefore (?) koalas are marsupials.  (How about platypuses?  Kuckaburras? Dingos?)

   So, claim 1. is deductive; claim 2. is inductive.  Claim 3. is simply invalid, since the information given leads to no conclusion at all; the information does not state that the only reason he does or does not play video games depends on his homework habits.


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