## Subjective Logic

by Audun Jøsang

Belief Reasoning with Subjective LogicSubjective logic is a calculus for subjective and uncertain beliefs. It can for example be used for modeling subjective trust networks, for modelling subjective Bayesian networks, for inteligence analysis and for subjective logical argumentation. In general, subjective logic is suitable for modeling and analysing situations involving uncertainty, incomplete knowledge and different world views. It generalises Bayes' theorem applied to uncertain probabilities

General beliefs are represented as

subjective opinionswhich are the input/output arguments in subjective logic. An opinion can express trust in a source or it can express belief about states/propositions. Binomial opinions are equivalent to Beta probability density functions, and multinomial opinions are equivalent to the more general Dirichlet probability density functions. This makes subjective logic suitable for reasoning with evidence represented as Beta or Dirichlet probability density functions. For details and theory see the the book on subjective logic or the Wikipedia subjective logic page.

Subjective Logic Demonstrations

- See interpretations of binomial opinions with the belief visualisation demo.
- Play with subjective logic operators.
- Analyse a simple trust network with subjective logic.
- Excel spreadsheet for 3x3 conditional deduction and abduction

Book on Subjective LogicTutorial on subjective logic given at FUSION 2016 in Heidelberg, July 2016.

Subjective Logic: A Formalism for Reasoning Under Uncertainty, 1st edition 2016. The book is available from multiple online stores inlcuding Springer and Amazon.com (US), Amazon.cn (China), Amazon.co.uk (GB), Amazon.de (Germany/EU), or Amazon.in (India).This book describes the subjective opinion representation, decision making with subjective opinions and the various subjective logic operators. The book also describes relevant applications of subjective logic in the areas of computational trust networks and Bayesian networks, which when combined represent

subjective networks.In a world where fake news and alternative facts have gone mainstream, subjective logic gives each individual the necessary tools to reason about the relative trustworthiness of information sources and the reliability of the information they provide. The possibility that information sources can be subjective and deceptive must be realistically considered in order to safely navigate and find order in the chaos of online media.

When trying to correctly perceive the reality around you, be aware that the truth you see is mostly subjective, and that objective truth is an endangered species which can be very hard to spot. Subjective truth might help us as individuals or groups to locally prosper and reach our goals. However, in the long term it's detrimental to the stability of the global civilisation when we hold and promote different and conflicting subjective truths.

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Last Updated 1 February 2017