Grounding the Lexical Substitution Task in Entailment

Existing definitions of lexical substitutes are often vague or inconsistent with the gold annotations. We propose a new definition which is grounded in the relation of entailment; namely, that the sentence that results from the substitution should be in the relation of mutual entailment with the original sentence. We argue that the new definition is well-founded and supported by previous work on lexical entailment. We empirically validate our definition by verifying that it covers the majority of gold substitutes in existing datasets. Based on this definition, we create a new dataset from existing semantic resources. Finally, we propose a novel context augmentation method motivated by the definition, which relates the substitutes to the sense of the target word by incorporating glosses and synonyms directly into the context. Experimental results demonstrate that our augmentation approach improves the performance of lexical substitution systems on the existing benchmarks. Context Ct Substitute w Cw |= Ct Ct |= Cw Meaning preserved I am glad to be out of the favor-trading scene for half a minute moment No No No It didn't seem like we had a lot of holes to fill. It's good, it gives us something we didn't have and we didn't lose much. award No Yes No Walking out of the church , a little gust of cold air caught me by surprise. icy No Yes No "It's a long way to anywhere worth going," he said. declare No Yes No Taste , hearing and touch became a single blur , and I do not know if my eyes were open. uncovered No No No My favorite thing about her is her straightforward honesty and that her favorite food is butter. uncomplicated No No No I had almost forgotten the body lying with broken neck on the cathedral's hard tiles damage Yes No No A black hallway opened into a space like a cathedral. The vault rose into obscurity above me, and a massive window stood ahead of me. large church Yes No No A black hallway opened into a space like a cathedral. The vault rose into obscurity above me, and a massive window stood ahead of me.