  Word sense disambiguation assumes word senses. Within the lexicography and
linguistics literature, they are known to be very slippery entities. The paper
looks at problems with existing accounts of `word sense' and describes the
various kinds of ways in which a word's meaning can deviate from its core
meaning. An analysis is presented in which word senses are abstractions from
clusters of corpus citations, in accordance with current lexicographic
practice. The corpus citations, not the word senses, are the basic objects in
the ontology. The corpus citations will be clustered into senses according to
the purposes of whoever or whatever does the clustering. In the absence of such
purposes, word senses do not exist.
  Word sense disambiguation also needs a set of word senses to disambiguate
between. In most recent work, the set has been taken from a general-purpose
lexical resource, with the assumption that the lexical resource describes the
word senses of English/French/..., between which NLP applications will need to
disambiguate. The implication of the paper is, by contrast, that word senses
exist only relative to a task.
