“… the most frequent words account for 85 percent of speech.”  p. viii

“Given that verbs typically account for 20 percent of all words in a language, this [focusing on just the most frequent verbs] may be a good strategy. Also, a focus on function words may be equally rewarding – 60 percent of speech in English is composed of a mere 50 function words.”  p. viii

“…verbs are in general more common in conversation, which tends to express feelings and opinions more than presenting information about objects and processes.”  p. 148

A Frequency Dictionary of Spanish: Core Vocabulary for Learners, by Mark Davies (also available in other languages)