Moore's Paradox

Moore's paradox concerns the putative absurdity involved in asserting a first-person present-tense sentence such as 'It's raining but I don't believe that it is raining' or 'It's raining but I believe that it is not raining'. The first author to note this apparent absurdity was G.E. Moore. These 'Moorean' sentences, as they have become known:

1. can be true,
2. are (logically) consistent, and moreover
3. are not (obviously) contradictions.
   

The 'paradox' consists in explaining why asserting a Moorean sentence is (or less strongly, strikes us as being) weird, absurd or nonsensical in some way. The term 'Moore's Paradox' is due to Ludwig Wittgenstein, who considered it Moore's most important contribution to philosophy. Wittgenstein devoted numerous remarks to the problem in his later writings, which has brought Moore's Paradox the attention it might otherwise not have received. Subsequent commentators have further noted that there is an apparent residual absurdity in asserting a first-person future-tense sentence such as 'It will be raining and I will believe that it is not raining'.

Moore's Paradox has also been connected to many other of the well-known logical paradoxes including, though not limited to, the liar paradox, the knower paradox, the unexpected hanging paradox, and the Preface paradox.

There is currently no generally accepted explanation of Moore's Paradox in the philosophical literature. However, while Moore's Paradox has perhaps been seen as a philosophical curiosity by philosophers themselves, Moorean-type sentences are used by logicians, computer scientists, and those working in the artificial intelligence community, as examples of cases in which a knowledge, belief or information system is unsuccessful in updating its knowledge/belief/information store in the light of new or novel information.