Abstract
In this paper, the authors try to answer the basic lexicographical question: how do we know whether a particular word is a mere word form, or a new lexeme that should thus be assigned an individual entry in a dictionary? The issue of negation in Czech (namely negative forms of nouns, adjectives, adverbs and verbs) serves them as a perfect example. They introduce two criteria for the choice of dictionary entries, the frequency criterion and the grammatical category criterion, and show how the negation of the parts of speech examined differs and what the implications are for lexicographers.