Validity is that feature of arguments or chains of reasoning studied by the science of logic. The notion of validity may be defined in two ways. The first uses the notion of truth: an argument is valid if the truth of its conclusion is guaranteed by the truth of its premises. The second appeals to basic accepted patterns of reasoning or principles of inference, for example that given 'A' and 'If A then B' one may infer 'B': a conclusion validly follows from certain premises if it can be derived from them in accordance with basic principles. A central question in modern work in logic is whether a complete set of principles of reasoning can be specified, so that any argument valid in the first sense is also valid in the second. Research Validity