英语中数词主要分为基数词和序数词两类.
基数词 ：表示数目的词称为基数词.其形式如下：
（1）．从1——10 one,two,three,four,five,six,seven,eight,nine,ten．
（2）．从 11——19 eleven,twelve,thirteen,fourteen,fifteen,sixteen,seventeen,eighteen,nineteen．
这里除 eleven,twelve,thirteen,fifteen,eighteen为特殊形式外,fourteen,sixteen,seventeen,nineteen都是由其个位数形式后添加后缀-teen构成.
（3）．从 21——99 整数几十中除twenty,thirty,forty,fifty,eighty为特殊形式外,sixty,seventy,ninety都是其个位数形式后添加后缀-ty构成.表示几十几时,在几十和个位基数词形式之间添加连字符“-” 21 twenty-one 76 seventy-six
（4）．百位数 个数基数词形式加“hundred”,表示几百,在几十几与百位间加上and．
101 a hundred and one 320 three hundred and twenty 648 six hundred and forty-eight
（5）．千位数以上 从数字的右端向左端数起,每三位数加一个逗号“,”.从右开始,第一个“,”前的数字后添加 thousand,第二个“,”前面的数字后添加 million,第三个“,”前的数字后添加 billion.然后一节一节分别表示,两个逗号之间最大的数为百位数形式.
2,648 two thousand six hundred and forty-eight
16,250,064 sixteen million two hundred and fifty thousand sixty-four
5,237,166,234 five billion,two hundred and thirty-seven million,one hundred and sixty-six thousand,two hundred and thirty-four
（6）．基数词在表示确切的数字时,不能使用百、千、百万、十亿的复数形式；但是,当基数词表示不确切数字,如成百、成千上万,三三两两时,基数词则以复数形式出现.
There are hundreds of people in the hall． 大厅里有数以百计的人.
Thousands and thousands of people come to visit the Museum of Qin Terra-Cotta Warriors and Horses every day． 每天有成千上万的人来参观秦兵马涌博物馆.
They went to the theatre in twos and threes． 他们三三两两地来到了剧院.
（7）．表示人的不确切岁数或年代,用几十的复数形式表示.
He became a professor in his thirties． 他三十多岁时成为了教授.
She died of lung cancer in forties． 她四十来岁时死于肺癌.
It was in the 1960s． 那是在二十世纪六十年代.
（8）．基数词的句法功能
基数词在句中可作主语、宾语、定语、表语、同位语.
The two happily opened the box． 两个人高兴地打开了盒子.（作主语）
I need three altogether． 我总共需要三个.（作宾语）
Four students are playing volleyball outside． 四个学生在外面打排球.（作定语）
We are sixteen． 我们是16个人.（作表语）
They three tried to finish the task before sunset． 他们三个人尽力想在日落前完成任务.（作同位语）
这是一些基数词的写法：
0 nought;zero;O
1 one
2 two
3 three
4 four
5 five
6 six
7 seven
8 eight
9 nine
10 ten
11 eleven
12 twelve
13 thirteen
14 fourteen
15 fifteen
16 sixteen
17 seventeen
18 eighteen
19 nineteen
20 twenty
21 twenty-one
22 twenty-two
23 twenty-three
30 thirty
32 thirty-two
40 forty
50 fifty
60 sixty
70 seventy
80 eighty
90 ninety
100 one hundred
101 one hundred and one
156 one hundred and fifty-six
192 one hundred and ninty-two
200 two hundred
300 three hundred
400 four hundred
500 five hundred
600 six hundred
700 seven hundred
800 eight hundred
900 nine hundred
1,000 one thousand
1,001 one thousand and one
1,300 thirteen hundred;one thousand and three hundred
2,000 two thousand
2,034 two thousand and thirty-four
6,502 six thousand five hundred and two
38,000 thirty-eight thousand
45,672 forty-five thousand six hundred and seventy-two
500,000 five hundred thousand
1,000,000 one million
3,123,400 three million,one hundred and twenty-three thousand and four hundred
8,000,000 eight million
47,000,000 forty-seven million
900,000,000 nine hundred million
1,000,000,000 a milliard,one milliard(美作:a billion,one billion)
1,050,000,000 one billion and fifty million
10,000,000,000 ten billion
200,000,000,000 two hundred billion
1,000,000,000,000 a billion,one billion(美作:a trillion,one trillion)
6,000,000,000,000 six million milliond
基数词和序数词的变化规则口诀
变化口诀1：
一、二、三,单独记；八去t,九除e,ve要用f替,整十基数变序数,先把ty变成tie；要是遇到两位数,十位基数个位序,th最后加上去。
变化口诀2：
基变序，容易记，加上th就可以；
一二三，特殊记，词尾字母tdd；
八减t，九减e，f来把ve替；
若是遇到整十数，ty变作tie;
若是遇到几十几，只变个位就可以。
解析：
1、one,two,three这三个变为序数词分别是first，second，third，这三个需单独记忆。
2、从第四开始，基数词变为序数词都要加th。
3、eight变为序数词的.'时候少个t不加只加h;nine变为序数词要去掉e再加th。
4、ve结尾的单词five和twelve变为序数词时要把ve改为f，再加th。
5、y结尾的单词即整十数的单词要把y变为ie，再加th。
6、如果把几十几的数变为序数词，只把个位上的数变为序数词就可以。
举例说明：
1-10的序数词：first，second，third，fourth， fifth， sixth， seventh. eighth， ninth， tenth.
11-19的序数词：eleventh, twelfth, thirteenth, fourteenth, fifteenth, sixteenth, seventeenth, eighteenth, nineteenth.
21-29的序数词：twenty-first, twenty-second, twenty-third, twenty-fourth, twenty-fifth, twenty-sixth, twenty-seventh, twenty-eighth, twenty-ninth.
20-90整十的序数词：twentieth, thirtieth, fortieth, fiftieth, sixtieth, seventieth, eightieth, ninetieth.
100序数词：one hundredth.
