The parts of speech which are most frequent are nouns and verbs. Every sentence must have a noun and verb. The exception is imperatives in which the pronoun "you" is understood as in "Come here!" To calculate the approximate frequency of parts of speech in English, I analyzed a part of the introduction of the book "The World's Greatest Chess Games." The part which I analyzed was 100 words long which was very convenient for calculation. Here it is:
The aim of this book is simple: to present the 112 greatest chess games of all time, with annotations that enable chess enthusiasts to derive the maximum enjoyment and instruction from them.
The first problem we faced was the selection of the games: how could we choose just 112 from the treasure-house of chess history? Clearly the games should be great battles, featuring deep and inventive play. We decided that the prime consideration had to be the quality of the play, not just of the winner, but of the loser. We rejected games where the loser offered little resistance.
I then counted the number of occurrences of each part of speech. Here are the results:
Nouns occurred more frequently than any other part of speech. However, adjectives occurred more frequently than verbs, 26% to 16%. It must be noted that articles were counted as adjectives because articles are not a part of speech. If articles are classified apart from adjectives, the number of occurrences of adjectives decreases to only 12. The only part of speech which never occurred was interjections.
More occurrences of adjectives than verbs were recorded, but this is because articles were included with adjectives. If treated separately, the number of verbs was greater than that of adjectives. It appears that articles are very common. Interjections, on the other hand, are not. The number of prepositions was high but this was because the infinitive marker "to" was classified as a preposition. If it had simply been classified as a part of the infinitive and thus a verb, the number of prepositions would have been much lower. The most common parts of speech were nouns, adjectives and verbs.