The semantic concepts of entailment and contradiction are central to all aspects of natural language meaning (Katz, 1972;van Benthem, 2008), from the lexicon to the content of entire texts.
natural language inference (NLI) -characterizing and using these relations in computational systems (Fyodorov et al., 2000;Condoravdi et al., 2003;Bos and Markert, 2005;Dagan et al., 2006;MacCartney and Manning, 2009) -is essential in tasks ranging from information retrieval to semantic parsing to commonsense reasoning.