Jonathan Campbell and Vladimir Lifschitz
Formalizations of commonsense knowledge rely on highly simplified representations of the world. After a conclusion is justified on the basis of one such representation in a nonmonotonic logic, it may not remain valid when additional relevant facts are taken into account to bring the formalization to a closer approximation of reality. However, if the conclusion continues to hold in the enriched theory, we can consider it to be reinforced. An argument in support of a claim can be represented by a sequence of nonmonotonic theories, each containing and enhancing the previous theory in the sequence and each entailing the claim. This idea is illustrated here by a sequence of formalizations of "Sam’s Calculus -- an example of commonsense reasoning due to Ernie Davis -- in the language of the Causal Calculator.