一、强调语气不同。
1、also一般用于肯定句，有强调意味，位于主谓语之间，即实义动词之前，助动词之后。
如：I can also do it.
我也能干那个活。
2、as well多用于口语，一般不用否定句，通常放在句末，强调时可放在句中。
如：He is a teacher, and a writer as well.
他是个教师，也是个作家。
二、用法不同。
1、also
adv. (副词)
1）also是较正式的用词，多用于书面语，基本意思是“也”“还”,表示两件事的性质相近或两件事情发生的时间相同，也可表示刚说过的话也适用于另一个人或物。在句中起补充追加的作用。
2）also主要用于肯定句和疑问句。在书面语中,also偶可用在no,nothing或其他带有否定意义的词之前，而在否定词之后则不能用also,而要用either(但not also可用于反诘疑问句或修辞疑问句，偶尔也用于陈述句)。
3）also多位于实义动词之前，非实义动词或第一个非实义动词之后,有时可放在整个谓语动词之前,间或用于句末。偶尔为了加强语气, also还可放在句首。also在句中位置不同常会影响句子的意思。
4）also直接置于一周各日之前,表示同样事件在不同日期发生过,习惯上不用介词。
5）not only...but also结构连接两个并列的成分或句子，意思是“不但…而且”。本结构中的谓语动词的数通常根据邻近原则,与最靠近的一个主语保持一致。本结构连接两个并列的句子时not only须位于句首，句子的主语和谓语须采用倒装语序。
6）also不用于比较等级。
2、as well as
1）as...as结构多用于肯定式，偶尔也可用于否定式。表示同样意思的否定式多用so...as。as...as结构用于否定句时多用于口语，侧重“像…一样”；so...as结构则多用于书面语，侧重“像…那样”。
2）as...as结构表示的是同级比较，第一个as后的形容词或副词不可用比较级，必须用原级，比较的对象亦须属同类。
3）as...as结构表示数量或程度时，可用于“as much+(不可数名词+) as”或“as many+(可数名词复数+) as”结构。
4）修饰as...as结构的常见词语有nearly,almost,just,exactly,half,quite,表示倍数或次数的形容词，“数词+times”等。这些修饰语都放在as...as结构之前。
5）使用as...as结构时，若第一个as后的名词是单数可数名词并有形容词修饰，则应使用“as+ adj.+ a/an+ n. ”结构，即不定冠词应位于形容词和名词之间。第二个as后面的名词或代词的格不同，意思也不同。
三、读音不同。
1、also的英式读法是[əz]；美式读法是[əz]。
2、as well as的英式读法是[æz wel æz]；美式读法是[æz wɛl æz]。
too 用于句末.I like English,too.
either只用于否定句.I don't like English,either.
as well(as)用于肯定句的句末.I like English as well.
I like Englishas well as math.=I like English,and I like math as well.
一、as well 用法：
1、as well常用作状语,作“又；也”解,相当于too或also,常位于句末,无须用逗号与句子分开.如：
I am going to London and my sister is going as well（＝going,too）.
我要到伦敦去,我妹妹也要去.
I not only play the guitar,I sing as well（＝I also sing ）.
我不但弹吉他,而且还演唱.
2、as well 在口语中也可用于句中,作“也好,也行”或“倒不如”解,用来缓和语气.如：
You may as well go、
你去也好.
The weather was so bad that we might（just）as well have stayed at home.
天气太坏了,早知道如此,倒不如呆在家里为好.
3、as well 可以直接用于just后,用作应答语（可视为It's just as well、的省略）,作“幸亏,幸而；无妨；没关系”解.如：
—We were too late to see the film.
我们去得太晚了,没有看上电影.
—Just as well、I hear it isn't very good.
不必遗憾,我听说电影也不怎么样.
二、as well as 用法
1、as well as常用来连接两个并列的成分,作“也,还”解.它强调的是前一项,后一项只是顺便提及.因此连接并列主语时,谓语动词与前一项一致；而用not only ...but also...连接时,谓语动词与后一项一致.如：
Your wife as well as you is friendly to me.
不仅你而且你的妻子也对我很友好.
（＝Not only you but also your wife is friendly to me、）
Electric energy can be changed into light energy as well as into sound energy.
电能既可以被转变成声能,又可以被转变成光能.
2、as well as 用来表示同级比较,指“一样好”.如：
You look as well as you did ten years ago.
你的身体看起来还和十年前一样好.
He plays the guitar as well as you.
他的吉他弹得和你一样好.本回答被提问者采纳
99年高考11小题 __ you've got a chance,you might as well make full use of it .
A Now that B After C Althopugh D As soon as
大部分学生对此题意思弄不太清楚，主要是对as well理解得不对，造成失误。现把as well的用法简单总结如下：
一、as well常用于肯定句句尾，表示“还，也”等意思。
1.He knows French,and he knows English as well.
他懂法语，他也懂英语。
2.Wang Hai is a worker and a militiaman as well.
王海是个工人，也是个民兵。s
二、as well后接as，边接两个同类项，表示“不但，而且，和跟”等意思，强调as well前面的人或事物。
1.He came as well as his brother.
不仅他哥哥来了，而且他也来了。
2.He gave me clothes as well as food.
他既给我食物，又给我衣服。
三、as well as和动词连用，表示同类事物相比较，结果一样好。
1.He can speak English as well as you do.
他英语说得和你一样好。
2.She sings as well as her sister.
她和她姐姐唱得一样好。
also的用法
also用于实义动词之前
▲also用于实义动词之前
They also agree with me.
他们也同意我的看法。
I also began to be interested in crickets.
我也开始对板球运动感到兴趣。
also用于be动词之后
▲also用于be动词之后
I was also there.
我也在那儿。
He is also an American.
他也是美国人。
also用于第一个助动词之后
▲also用于第一个助动词之后
His sister has also gone to town.
他的妹妹也到镇里去了。
The leisure center has also proved uneconomic.
休闲中心业已证明利润不大。
also有时放在句首
▲also有时放在句子的最前
Also, some students were tempted to add written comment of their own throughout the paper.
一些学生也冒险通过论文写出他们自己的评论。
I thought it was the perfect answer. Also, Tony and I had never done a historical subject.
我认为它是完美的答案。而且，托尼和我从没有作过历史科目。
also不能放在句末