Humans do not reason from contradictory premises. The psychological aspects of paraconsistency.

The creation of paraconsistent logics have expanded the boundaries of formal logic by introducing coherent systems that tolerate contradictions without triviality. Thanks to their novel approach and rigorous formalization they have already found many applications in computer science, linguistics and mathematics. As a natural next step, some philosophers have also tried to answer the question if human everyday reasoning could be accurately modelled with paraconsistent logics. The purpose of this article is to argue against the notion that human reasoning is paraconsistent. Numerous findings in the area of cognitive psychology and cognitive neuroscience go against the hypothesis that humans tolerate contradictions in their inferences. Humans experience severe stress and confusion when confronted with contradictions (i.e., the so-called cognitive dissonance). Experiments on the ways in which humans process contradictions point out that the first thing humans do is remove or modify one of the contradictory statements. From an evolutionary perspective, contradiction is useless and even more dangerous than lack of information because it takes up resources to process. Furthermore, it appears that when logicians, anthropologists or psychologists provide examples of contradictions in human culture and behaviour, their examples very rarely take the form of: (p and ¬p). Instead, they are often conditional statements, probabilistic judgments, metaphors or seemingly incompatible beliefs. At different points in time humans are definitely able to hold contradictory beliefs, but within one reasoning leading to a particular behaviour, contradiction is never tolerated

ON THE INTENTIONALITY AND IMPERFECT BUT MINIMAL RATIONALITY OF HUMAN SPEAKERS

I will criticize the current logical analysis of attitudes due to J. Hintikka (1971) according to which human agents are either perfectly rational or completely irrational. I will present the principles of a general logic of first level attitudes and actions that accounts for our intentionality and imperfect but minimal rationality. First level attitudes and actions are attitudes and actions of individual agents at a single moment of time. In my approach psychological modes of propositional attitudes have other components than their basic Cartesian category of cognition and volition. I will formulate a recursive definition of the set of all psychological modes. I will also analyze the nature of complex first level attitudes such as conditional attitudes and sums and denegations of attitudes which are irreducible to propositional attitudes. My primary purpose here will be first to explicate inductively conditions of possession and of satisfaction of all first level attitudes and to integrate my logic of attitudes within a general theory of first level actions explicating the primacy of intentional actions, their conditions of success and fundamental laws of action generation. For that purpose I will use a non classical predicative propositional logic and consider subjective as well as objective possibilities. Agents of voluntary actions and illocutionary acts have intentions and other first level attitudes. I will explain why logically equivalent propositions are not the content of the same attitudes and intentional actions and why human agents are neither logically omniscient nor perfectly rational but always remain minimally rational in the exercise of thought and the use of language. For more information see my next book Speech Acts in Dialogue