oletuslogiikan

Oletuslogiikka, also known as default logic, is a non-monotonic reasoning system developed by Raymond Reiter. It aims to formalize the process of reasoning with default assumptions, where certain conclusions are drawn unless there is evidence to the contrary. This contrasts with classical logic, which is monotonic, meaning that adding new information never invalidates existing conclusions.

In default logic, a default rule typically takes the form "if P is true, and it is consistent to assume Q is true, then conclude Q." Here, P is the prerequisite, and Q is the consequent. The crucial element is the consistency check: Q is only concluded if assuming its truth does not lead to a contradiction within the given knowledge base. This allows for plausible reasoning, where conclusions are tentative and can be revised in light of new information that contradicts the default assumption.

Default logic is applied in areas such as artificial intelligence, particularly in knowledge representation and reasoning systems. It is useful for modeling situations where complete information is unavailable, and agents must make educated guesses. For instance, knowing that birds typically fly, one might use a default rule to conclude that a specific bird can fly. However, if it is later learned that the bird is a penguin, this default conclusion would be retracted. The formalization of such non-monotonic inferences is a key contribution of default logic.