Editing Word-sense disambiguation (section)

===Discreteness of senses===
Finally, the very notion of "[[word sense]]" is slippery and controversial. Most people can agree in distinctions at the [[coarse-grained]] [[homograph]] level (e.g., pen as writing instrument or enclosure), but go down one level to [[fine-grained]] [[polysemy]], and disagreements arise. For example, in Senseval-2, which used fine-grained sense distinctions, human annotators agreed in only 85% of word occurrences.{{sfn|Edmonds|2000|pp=}} Word meaning is in principle infinitely variable and context-sensitive. It does not divide up easily into distinct or discrete sub-meanings.{{sfn|Kilgarrif|1997|pp=91–113}} [[Lexicography|Lexicographers]] frequently discover in corpora loose and overlapping word meanings, and standard or conventional meanings extended, modulated, and exploited in a bewildering variety of ways. The art of lexicography is to generalize from the corpus to definitions that evoke and explain the full range of meaning of a word, making it seem like words are well-behaved semantically. However, it is not at all clear if these same meaning distinctions are applicable in [[Computational science#Applications of computational science|computational applications]], as the decisions of lexicographers are usually driven by other considerations. In 2009, a task – named [[lexical substitution]] – was proposed as a possible solution to the sense discreteness problem.{{sfn|McCarthy|Navigli|2009|pp=139–159}} The task consists of providing a substitute for a word in context that preserves the meaning of the original word (potentially, substitutes can be chosen from the full lexicon of the target language, thus overcoming discreteness).