also、as well 和 too 三者都为副词，意思很相近，相当于 in addition，可以意为“还，也”，also 比 as well 和 too 更正式。
一、Also 在写作中很常见，但在口语中很少见，可以出现在句子的不同位置，通常置于主要动词之前， 情态动词或第一助动词或 be 动词之后，例如：
主要动词之前：
We also improved our customer satisfaction levels.
我们也提高了顾客满意的标准。
助动词 be 之后：
The reduced consumer demand is also affecting company profits.
消费需求的降低也影响到了公司的利润。
第一助动词 have 之后：
I’ve been working in the garden this week, and I’ve also been reading a lot.
这周我在花园里工作，也读了很多书。
情态动词之后：
Our students can also opt to stay in residence.
我们的学生也可以选择住校。
Also 还可以放在句首，用来强调接下来的或是开启一个新的话题，例如：
It’s very humid. Also, you can easily get sunburnt.
天气很潮湿。而且，你很容易被晒伤。
OK, I’ll phone you next week and we can discuss it then. Also, we need to decide who will be going to Singapore.
好吧，我下周给你打电话，到时候再讨论。另外，我们需要决定谁将去新加坡。
当 also 置于句末的时候，通常用 too 或 as well 代替，例如：
She contacted him in the office but he didn’t answer the phone. His mobile phone was silent too/as well.
她在办公室联系了他，但他没有接电话。他的手机也没有声音。
二、as well 在口语中比 also 更常见，而且经常出现在句末，例如：
He should pay and maintain you as well.
他得给你钱，还得供养你。
We should stick to the principles and be flexible as well.
既要有原则性，也要有灵活性。
三、too 通常也放在句末，例如：
Gill’s having chicken. I’ll probably have chicken too.
吉尔在吃鸡肉。我可能也要鸡肉。
She looks really tired and she must be really hungry too.
她看起来很累，一定也很饿。
当直接指向主语时，too 可以直接跟在主语后面，这时它通常不出现在情态动词或助动词后面，而且经常前后用逗号隔开，例如：
I too thought she looked unwell.
我也觉得她看起来不舒服。
We, too, have been very pleased to receive the prize on her behalf.
我们也很高兴代表她领奖。
解析：此句不能改成 We have too been very pleased to receive the prize on her behalf.
相比于 also 和 as well，too 更常见于对诸如表达美好愿望等固定表达的回应，以及由单个宾语代词组成的回应，例如：
A: Enjoy the play.
好好欣赏这出戏。
B: Thanks. You enjoy your evening too.
谢谢。你也喜欢你的夜晚。
解析：You enjoy your evening too 比 Your enjoy your evening also. 和 You enjoy your evening as well. 常用。
A: I need to go to the gym.
我要去健身房。
B: Yeah, me too.
是的，我也是。
解析：Yeah, me too. 比 Yeah, me also. 和 Year, me as well. 常用。
在祈使句中， as well 和 too 比 also 更常用，例如：
Give me a book of ten first and a book of ten second as well then please.
请先给我一本十岁的书，再给我一本十岁的书。