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Philosophy 103: Introduction to Logic
How to Construct a Truth Table
Abstract: The general principles for the construction of truth tables are explained and illustrated.
- How to construct the guide columns:
- Write out the number of variables (corresponding to the number
of statements) in alphabetical order.
- The number of lines needed is 2n where n is the number
of variables. (E. g., with three variables, 23 = 8).
- Start in the right-hand column and alternate T's
and F's until you run out of lines.
- Then move left to the next column and alternate pairs of
T's and F's until you run out of lines.
- Then continue to the next left-hand column and double the
numbers of T's and F's until completed.
- Example: construct a truth table for p
( q r )
|
Line
No.
↓
|
I, A
variables in alphabetical
order
↓ |
|
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|
|
III, A
First
line
all T
→
|
|
p |
q |
r |
q r |
p
(q r) |
1 |
T |
T |
T |
T |
T |
I, B
number of lines
= 2n
→
III, D
half T's
half F's |
2 |
T |
T |
F |
T |
T |
3 |
T |
F |
T |
T |
T |
4 |
T |
F |
F |
F |
T |
5 |
F |
T |
T |
T |
T |
6 |
F |
T |
F |
T |
T |
7 |
F |
F |
T |
T |
T |
8 |
F |
F |
F |
F |
F |
|
III, B
last
line
all F
|
↑
I, E
alternate
double of previous
T and F |
↑
I, D
alternate
pairs of
T and F
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↑
I, C
alternate
T and F
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- As check that the guide columns were done correctly:
- The first horizonal line will be all T's.
- The last horizonal line will be all F's.
- The left-most column will be evenly divided; the first half
all T's and the second half all F's.
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