ABSTRACT
This chapter describes a method, the deductive method, which can be used to construct, or to demonstrate the validity of, valid quantificational arguments. It examines the concepts of validity and invalidity in their application to quantificational argument forms. The chapter begins by repeating the definition of validity and invalidity for argument forms in general which was given in TFL. A form of argument is said to be valid if there is no possible exemplification in which the premisses are all true but the conclusion is false. It is invalid if in at least one possible exemplification all the premisses are true but the conclusion is false. A rule of deduction is valid if it allows deduction in accordance with a valid argument form. However, the principle underlying the rule can be stated fairly easily and can be illustrated in a simple case.
