英語序數(shù)詞前面不一定都要加the，應視情況而定。當序數(shù)詞單純地表示“第幾”的時候就加the，當序數(shù)詞用于“又一”的意思時則用a，當序數(shù)詞前有人稱代詞時，不加the。

序數(shù)詞什么情況下不加the

1．當序數(shù)詞前有形容詞性物主代詞或名詞所有格修飾時,序數(shù)詞前不用the.

Mother was my first teacher in my life.媽媽是我生命中的第一個老師.

Tom is Lily's third boyfriend.湯姆是莉莉的第三個男朋友.

2．當表達分數(shù)時,序數(shù)詞前不用the.

One fifth of the students here are from the country.這兒1/5的學生來自農村.

Three fourths of the students here are from the country.這兒的3/4的學生來自農村.

3．當表達“又一,再一”時,序數(shù)詞前不用the,但可加不定冠詞.

Please give me a second chance.請再給我一次機會.

The poor woman had a third baby.那個可憐的婦女又生了第三個寶寶.

4．當表達“年月日”時,尤其在朗讀時,序數(shù)詞前要加the.

He was born on June 6th,1974.他出生在1974年6月6日.

5．當序數(shù)詞在句中作狀語時,序數(shù)詞前不用the.

Who got there second?誰第二個到那兒的?

I finished the work first.我最先完成那項工作.

6.當表達考試（賽跑等）中獲得的名次時,序數(shù)詞前不用the.

She stands first in her class.她在班上成績排名第一.