We are not so much concerned with defining the parts of speech as with enabling the student to recognize them in context. The definition of a noun (for example) only becomes meaningful after the student has seen and recognized many particular nouns in particular verb structures.
It should be noticed that the structural approach to the recognition and definition of parts of speech departs somewhat from the methods and terminology of traditional grammar. The student who is at all familiar with traditional English Grammar will need to approach the present treatment without preconceptions.
In accordance with their use in the sentence, words are divided into eight classes called parts of speech, - namely, nouns, pronouns, adjectives, adverbs, prepositions, conjunctions, and interjections.
- See more at: http://www.english4dummies.com/grammar/parts_of_speech.html#sthash.lBEWmGum.dpuf