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Title: The book is fine, but on page 125...
Review: On page 125 Bennet writes: "This [Modus Ponens] is a valid inference as long as the two premises are true". But the sentence should read: "This is a valid inference, and as long as the two premises are true the conclusion will be true".The original formulation is in fact mistaken. Modus Ponens, like all valid inferences, is valid also in the case in which the two premises are false.The standard definition of validity says that an argument is valid if and only if if the premises are true, then the conclusion must also be true. Since "if the premises are true, then the conclusion must also be true" is a conditional statement, it is true in the case in which its antecedent is false (and therefore the premises are false). So the original formulation confuses validity with truth.
