As my post on mechanics emphasizes, learning the parts of speech is crucial to understanding how to correctly revise your writing.  Most of you have heard each name of each part of speech.  The problem often arises when you are asked to identify certain parts of speech and how they function within a sentence.

Verbs denote actions, occurrences, or states of being.

Adjectives modify nouns or pronouns.

Adverbs modify any other part of language except nouns.

Prepositions introduce prepositional phrases, thus indicating a relation between things in the sentence.

Conjunctions connect words, phrases, or clauses.

Interjections are used to express strong feelings or emotions.

Take a look at the following scenario which demonstrates the advantage of being able to identify parts of speech and their functions within a sentence.

After I became ill, my mother took me to the hospital.  They placed me in a room and began an IV.

In this sentence, the pronoun, "they" is ambiguous.  A pronoun takes the place of a noun or another pronoun.  Can you identify a noun or a pronoun that "they" is replacing in this sentence?  No, because "they" is not replacing a noun or a pronoun, so its use here is incorrect.  "They" should be replaced with "The doctor" or "The nurse."