  We analyze the frequency-rank relationship in sub-vocabularies corresponding
to three different grammatical classes ({\em nouns}, {\em verbs}, and {\em
others}) in a collection of literary works in English, whose words have been
automatically tagged according to their grammatical role. Comparing with a null
hypothesis which assumes that words belonging to each class are uniformly
distributed across the frequency-ranked vocabulary of the whole work, we
disclose statistically significant differences between the three classes. This
results point to the fact that frequency-rank relationships may reflect
linguistic features associated with grammatical function.
