Monday, March 30, 2009

TRUTH TABLE

TRUTH TABLE


TRUTH TABLE is A convenient method for analyzing a compound statement is to make a truth table for it.
A truth table specifies the truth value of a compound proposition for all possible truth values of its constituent propositions.


The truth values “true” and “false” are respectively denoted by the letters T and F.






Truth Table:


Often we want to discuss properties/relations common to all propositions. In such a case rather than stating them for each individual proposition we use variables representing an arbitrary proposition and state properties/relations in terms of those variables. Those variables are called a propositional variablePropositional variables are also considered a proposition and called a proposition since they represent a proposition hence they behave the same way as propositions. A proposition in general contains a number of variables. For example (P  Q) contains variables P and Q each of which represents an arbitrary proposition. Thus a proposition takes different values depending on the values of the constituent variables. This relationship of the value of a proposition and those of its constituent variables can be represented by a table. It tabulates the value of a proposition for all possible values of its variables and it is called a truth table


For example the following table shows the relationship between the values of P, Q and P  Q: 


OR
PQ(P  Q)
FFF
FTT
TFT
TTT



















In the table, F represents truth value false and T true. 
This table shows that P  Q is false if P and Q are both false, and it is true in all the other cases. 

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