Different types of negation reshape logical reasoning with counterfactuals
Modus Tollens and Counterfactuals and Counterfactual Reasoning Based on Three Types of Negation
Artificial Intelligence
Summary
This paper looks at how a basic logical rule called Modus Tollens can change when using different kinds of negation, which is how logic expresses ’not’. The authors identify three types of negation—contradictory, opposite, and intermediary—and show how each leads to a different version of Modus Tollens. They then link these versions to ways people think about ’what if’ scenarios that contradict reality, called counterfactuals. Their work offers a way to understand and compute truth values for these logical forms, helping ensure reasoning stays consistent and accurate.
Modus Tollenscounterfactualsnegationcontradictory negationopposite negationintermediary negationlogical inferencetruth value algorithms
Authors
Zhenghua Pan
Abstract
Modus Tollens (MT) is a classical logical inference rule, while counterfactuals are hypothetical statements that are contrary to facts, and counterfactual reasoning is a process of reasoning based on counterfactuals. Negation is an indispensable core concept in them. In this paper, based on the logical systems LCOI&PLCOI with contradictory negation, opposite negation and intermediary negation, we propose three variants of Modus Tollens corresponding to distinct negation types, namely MTC: Modus Tollens based on contradictory negation, MTO: Modus Tollens based on opposite negation, and MTI: Modus Tollens based on intermediary negation. We define the implications within MTC, MTO and MTI, provide the truth value algorithms of MTC, MTO and MTI, and discuss the reducibility of these algorithms. To incorporate these three types of negation into counterfactuals and counterfactual reasoning, we differentiate counterfactuals into two types based on whether they possess logical negation, thereby proposing three counterfactuals and counterfactuals reasoning based on different logical negations. In this paper, we further argue that the three counterfactuals reasoning based on different logical negations have the same inference form as MTC, MTO and MTI, respectively. In other words, they share the same inference structure. As a result, the truth value algorithms for MTC, MTO and MTI can be as the truth value algorithms for the three counterfactuals reasoning based on different logical negations. The algorithms indicates that if the first premise of the reasoning is true, the truth values of the reasoning conclusions are identical to the truth values of the three negative premises in the reasoning premises, respectively. This reflects the consistency and accuracy of the truth value algorithms.