Truth Tables
A tabular device to obtain the truth value of a compound statement or to check the validity of a simple or compound statement is called a truth table.
The number of horizontal lines (called rows) in a truth table depends upon the number of substatement involved in the problem. If the problem involves n simple statements then the number of rows is 2^{n}, i.e.,
Number of statements

Number of rows

1

2^{1} = 2

2

2^{2} = 4

3

2^{3} = 8

In the first n vertical lines (called columns) we take all the possible situations of truth or falsehood of the substatements and in the later columns we indicate the truth values of the compound statements. The number of columns in a truth table depends upon the problem and there is no general rule for this.