八大詞類包括名詞(nouns)，代名詞(pronouns)，動詞(verbs)，形容詞(adjectives)，副詞(adverbs)，介系詞(prepositions)，連接詞(conjuctions)，與指定詞(determiners)。每種詞類皆有不同的功能與特性。
1. 名詞(nouns)：名詞可作主詞、受詞、補語、及同位語
例：1. Severe winter storms in the Northwest have caused many deaths.
(本句storms為主詞，Northwest為介系詞in的受詞，deaths為動詞caused的受詞，請注意，只有介系詞與動詞才會有受詞。)
2. John Smith, our English teacher, comes from Australia.
(John Smith為主詞，our English teacher為主詞同位語，Australia為from之受詞。)
3. The storm was a disaster. (主詞補語)
4. The book make him a famous person. (受詞補語)
2. 代名詞(pronouns)：代名詞包括主格(I, we, you, she, he, it, they)、所有格(my, our, your, her, his, its, their)，與受格(me, us, you, her, him, it, them)。主格當主詞，受格當動詞或介系詞之受詞，所有格則為形容詞的功用，後面接名詞。
例：1. If a lizard(蜥蜴) loses its tail, a new one grows to replace it.
2. They believe that their theory is based on facts.
3. We gave them the books.
3. 動詞(verbs)：動詞要特別注意單複數、時態、主動或被動。
例：1. In those days most areas did not have electrical service.
2. When his father came home, he had finished his work.
3. The problem will be solved someday.
4. There are hundreds of people attending the party.
4. 形容詞(adjectives)：形容詞主要是用來修飾名詞，或當作補語。
例：1. He is a dangerous person. (修飾person)
2. It is dangerous to take drugs. (吸毒)。 (作主詞補語)
3. A coral reef(珊瑚礁) is found only in warm, shallow seas(修飾seas)
4. The news made her happy. (受詞補語)
5. 副詞(adverbs)：副詞是用以修飾動詞、形容詞、副詞，及整個子句。
例：1. Fortunately, he passed the examination. (修飾後面整個子句)
2. The conditions are extremely dangerous. (修飾dangerous)
3. The building was designed by an internationally famous architect.. (修飾famous)
4. The reason why he died was not clearly understood. (修飾understood)
5. He had studied extremely hard, so he passed the examination. (修飾副詞hard)
6. 介系詞(prepositions)：結構上，介系詞後面應接名詞片語或動名詞。介系詞所引導的片語稱為介系詞片語，主要功能是當形容詞或副詞。
例：1. Only two trains left during the morning. (當副詞，修飾left)
2. In the spring of 1988, the artist left for Europe. (當副詞，修飾後面整句)
3. Scientists give us a lot of information about our environment. (當形容詞，修飾information)
7. 連接詞(conjunctions)：連接詞主要包括對等連接詞(and, or, but, yet, both… and…, neither…nor…, either…or…, not only… but also…等等)及從屬連接詞(如when, while, before, after, since, although, though, because, if等等)。對等連接詞的重點在於所引導的結構前後要平行對稱，而從屬連接詞則引導從屬子句。
例：1. The beggar was cold and hungry. (平行形容詞)
2. Helicopters(直昇機) can rise or descend vertically(垂直地). (平行動詞)
3. Benjamin Franklin was a well-known inventor, diplomat(外交家) and statesman(政治家). (平行名詞)
4. He is used to eating a lot but doing little exercise. (平行動名詞)
5. Because I am too busy, I can’t do it now.
6. He failed although he tried hard.
8. 指定詞(determiners)：指定詞是用以限定後面的名詞，包括some, every, this, that, these, those等等。我們要特別注意的是every, this, that後面接單數名詞，these與those接複數名詞，而some(一些)則可接單數不可數名詞或複數可數名詞。
例：1. In those days girls used to wear mini skirts.
2. Every story in this book is very interesting.
3. The boss bought some equipment to modernize his factory. (equipment“設備”為不可數名詞)
4. The witness(證人) offered the police some clues about the murder.
