Recognising Textual Entailment with Logical Inference

With the goal of producing explainable entailment decisions, and ultimately having the computer "understand" the sentences it is processing, we have been pursuing a (somewhat) "logical" approach to recognizing entailment. First our system performs semantic interpretation of the sentence pairs. Then, it tries to determine if the (logic for) the H sentence subsumes (i.e., is implied by) some inference-elaborated version of the T sentence, using WordNet (including logical representations of its sense definitions) and the DIRT paraphrase database as its sources of knowledge. For pairs where it can conclude or refute entailment, the system often produces explanations which appear insightful, but also sometimes produces explanations which are clearly erroneous. In this paper we present our system and illustrate its good and bad behaviors. While the good behaviors are encouraging, the primary challenges continue to be: lack of lexical and world knowledge; poor quality of existing knowledge; and limitations of using a deductive style of reasoning with imprecise knowledge. Our best scores were: 56.5% (2-way task) and 48.1% (3-way task)