A 1ST-ORDER CONDITIONAL LOGIC FOR PROTOTYPICAL PROPERTIES

An approach for representing knowledge about defaults and prototypical properties is presented. This is accomplished by adding to first-order logic a 'variable conditional' operator to express relations between entities and prototypical properties of such entities. Truth conditions for this operator are based on a possible-worlds semantics; a proof theory is provided, and the logic is shown to be sound and complete. Properties of the resultant formal system are argued to correspond to common intuitions concerning defaults and prototypical properties. Moreover the system is argued to provide a more appropriate basis for representing knowledge about such entities than other existing approaches.