Determine whether the argument is valid or invalid by comparing its symbolic form with the standard forms given in Tables 3.15 and 3.16. For each valid argument, state the name of its standard form.
If we serve salmon, then Vicky will join us for lunch. If Vicky joins us for lunch, then Marilyn will not join us for lunch. Therefore, if we serve salmon, Marilyn will not join us for lunch.
To identify:
Whether the given argument is valid or invalid by comparing its symbolic form with the standard forms given in Tables 3.15 and 3.16 and for each valid argument, state the name of its standard form.
Given information:
If we serve salmon, then Vicky will join us for lunch. If Vicky joins us for lunch, then Marilyn will not join us for lunch. Therefore, if we serve salmon, Marilyn will not join us for lunch.
Concept Involved:
An Argument and a Valid Argument: Anargumentconsists of a set of statements calledpremisesand another statement called theconclusion. An argument isvalidif the conclusion is true whenever all the premises are assumed to be true. An argument isinvalidif it is not a valid argument. A symbolic argument consists of a set of premises and a conclusion. It is called a symbolic argument because we generally write it in symbolic form to determine its validity.
A disjunction is a compound statement formed by joining two statements with the connector OR. The disjunction "p or q" is symbolized by A disjunction is false if and only if both statements are false; otherwise it is true. 
A conjunction is a compound statement formed by joining two statements with the connector AND. The conjunction "p and q" is symbolized by

A conditional statement, symbolized by

A biconditional statement is defined to be true whenever both parts have the same truth value. The biconditional operator is denoted by a doubleheaded arrow The biconditional represents "p if an only if q", where p is a hypothesis and q is a conclusion. 
Standard Forms:
Arguments can be show to be valid if they have the same symbolic form as an argument that is known to be valid. For instance, we have shown that the argument is valid.
This symbolic form is known asdirect reasoning. All arguments that have this symbolic form are valid.
Transitive reasoning can be extended to include more than two conditional premises. For instances, if the conditional premises of an argument are
Table 3.15 shows four symbolic forms and the name used to identify each form. Any argument that has a symbolic form identical to one of these symbolic forms is a valid argument.
Table 3.15 Standard Forms of Four Valid Arguments  
Direct Reasoning  Contrapositive Reasoning  Transitive Reasoning  Disjunctive Reasoning  
Table 3
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