In statement 6, there are only two possible cases, and the truth table is shown in [Table 5].
Table 5
| 1 | 1 and 1 = 6 |
| T | T |
| F | F |
We know that 6 is true if and only if 1 is true. In other words, the statement “1 and 1 if and only if 1” is true, no matter what statement 1 may refer to. It is because of this fact that we never use a statement in the form “1 and 1”: it can always be replaced by the plain statement “1.”
LOGICAL-TRUTH CALCULATION BY
EXAMINING CASES AND REASONING
Now you may say that this is all very well, but what good is it? Almost anybody can use these connectives correctly and certainly has had a great deal of practice using them. Why do we need to go into truth values and truth tables?
When we draft a contract or a set of rules, we often have to consider several conditions that give rise to a number of cases. We must avoid:
1. All conflicts, in which two statements that disagree apply to the same case.
2. All loopholes, in which there is a case not covered by any statement.
If we have one statement or condition only, we have to consider 2 possible cases: the condition satisfied or the statement true; the condition not satisfied or the statement false. If we have 2 conditions, we have to consider 4 possible cases: true, true; false, true; true, false; false, false. If we have 3 conditions, we have to consider 8 possible cases one after the other ([see Table 6]).