Simplicity, Complexity, Unexpectedness, Cognition, Probability, Information

by Jean-Louis Dessalles     (created 31 December 2008, updated June 2016)

Simplicity and necessity

The notion of necessity generalizes the notions of desires and beliefs. It measures how much a state of affairs is believed or wanted. It closely corresponds to the intuitive notion of ‘necessity’. Necessities are negative in case of disbelief or avoidance.

Necessity has two origins: emotional intensity and unexpectedness; reasoning is based on conflicting necessities.

Necessities represent beliefs or desires. They change sign through negation.

Necessities come from the negation of situations that are emotional and/or unexpected. A situation s may be ascribed necessity values νi(s) from two sources (Dessalles, 2008): Lastly, necessities may be propagated from consequence to cause (Dessalles, 2015). A given situation s may receive different necessity values from different sources. They may add up. However, when deciding about actions or beliefs, necessities of opposite sign create a cognitive conflict that leads to deliberative reasoning and argumentation (see Dessalles, 2015). During the deliberative procedure, necessities may be transferred from consequence to cause to propagate cognitive conflict.


Dessalles, J.-L. (2008). La pertinence et ses origines cognitives - Nouvelles théories. Paris: Hermes Science.

Dessalles, J.-L. (2015). A Cognitive Approach to Relevant Argument Generation. Computational Models of Natural Argument (CMNA-15). Bertinoro, I: .


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