Logic Worksheet With Answers Page 18
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22 Premises: the given statements.
Conclusion: the result determined by the truth of the premises.
If the conclusion is true whenever the premises are assumed to be true then it is a valid
argument. An invalid argument is also called a fallacy
Truth tables can be used to test validity:
1. Use a letter to label each statement in the argument;
2. Express the premises and the conclusion symbolically;
3. Construct the truth table and plot the conclusion on the last column;
4. Check each row were all the premises are True; if all of the corresponding true values on
the last column are also Ts, then the argument is valid; otherwise, is invalid.
Ex: If Mr. Teacher is explaining the lesson, then we all pass the Exam. On the next Exam we all
passed it.
Building the argument: If Mr. Teacher is explaining the lesson, then we all pass the Exam. On
the next Exam we all passed it. Therefore, if Mr. Teacher explains the lesson, we all pass the
Exam.
p: Mr. Teacher is explaining the lesson;
q: We all pass the exam
We write these symbolically:
p
q
(Premise 1)
q
(Premise 2)
p
(Conclusion)
The table is:
Premise 2
Premise 2
Conclusion
p
q
p
p
q
T
T
T
T
T
F
F
T
F
T
T
F
F
F
T
F
The argument is invalid, or a fallacy.
Standard Forms of Arguments
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