1.基數詞是表示數目的數字，如：

one(一), two(二), ten(十), twenty(二十), one hundred(一百), two thousand(兩千), ten million(一千萬), three billion(三十億)等。

2.基數詞可相當于名詞，可有復數形式,這時它所表達的數量不很準確,僅僅是一個大概范圍。hundred, thousand和million等的復數形式之后常接of片語，表示數以百計、千計、百萬計等;of片語有時也可省略。

I have found a way to make thousands of dollars.

我已經找到一個賺成千上萬美元的方法。

They arrived in twos and threes.

他們三三兩兩的來了。

Hundreds of lives were lost in the fire.

數百人在大火中喪生。

Thousands and thousands of people got infected with flu every year.

每年成千上萬的人受到流行性感冒感染。

In order to maintain its operation, the company needs millions of dollars.

這個公司需要數百萬美元以維持其運作。

3.dozen, score, hundred, thousand, billion, million之前有確定的數字時不論后面有無of，字尾都不加s。

It is two thousand of quarters, 250 dollars.

是兩千個25美分，250美元。

4.基數詞表示幾十的復數數詞的變化形式與名詞相同，一般用來表示人的不確切年齡。

I will become a famous painter in my twenties.

我將在二十歲時成為知名畫家。

He died in his early thirties.

他三十剛過就死了。

5.基數詞在句中可作主語、賓語、修飾語、主語補語和同位語。

Thirteen is an unpropitious number.

13是個不吉利的數字。

Seven is an odd number.

七是奇數。

基數詞Seven作主語。

I still need two.

我還需要兩個。

I need at least eight.

我至少需要八個。

基數詞eight作賓語。

Return those two coins to me!

把那兩枚硬幣還給我!

Thirty students are doing chemical experiments in this classroom.

三十個學生在這間教室里做化學試驗。

基數詞Thirty作修飾語。

Six plus two is eight.

六加二是八。

Four plus two is six.

四加二是六。

基數詞six作主語補語。

Have you ever seen us two?

你見過我們兩個人嗎?

基數詞two作賓語us的同位語。