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Question 415720:  If the argument below is valid, name which of th four valid forms of argument is represented. If it is not valid, name the fallacy that is represented. 
 If the water is filtered, then it does not contain lead. 
The water contains lead. 
Therefore, the water is not filtered. 
 Answer by Theo(13342)      (Show Source): 
You can  put this solution on YOUR website! argument is valid.
 
 
first statement says that if the water is filtered, then it does not contain lead.
 
 
second statement says the water contains lead.
 
 
conclusion is that the water is not filtered.
 
 
it cannot be filtered because it it was filtered it would not contain lead, but it does.
 
 
the four valid forms of argument are contained in the following reference:
 
 
http://commonsenseatheism.com/?p=3709
 
 
the four valid forms are:
 
 
MODUS PONENS
 
If p is true, then q is true 
p is true 
therefore q is true
 
 
MODUS TOLLENS
 
 
if p is  true, then q is true. 
q is not true. 
therefore p is not true
 
 
DILEMMA
 
 
either p or q are true 
if p is true, then r is true. 
if q is true, then r is true. 
therefore r is true.
 
 
SIMPLIFICATION
 
 
p and q are true 
therefore p is true
 
 
Of the 4 forms, I believe MODUS TOLLENS fits the best.
 
 
p is equal to "if the water is filtered then it does not contain lead" 
q is equal to "it does not contain lead" 
therefore the water is not filtered.
 
 
this is fairly obvious because if the water was filtered it would not contain lead.
 
 
if p is true then q is true 
q is not true (the water contains lead) 
therefore p is not true.
 
 
 
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