also、as well 和 too 三者都為副詞，意思很相近，相當於 in addition，可以意為「還，也」，also 比 as well 和 too 更正式。
一、Also 在寫作中很常見，但在口語中很少見，可以出現在句子的不同位置，通常置於主要動詞之前， 情態動詞或第一助動詞或 be 動詞之後，例如：
主要動詞之前：
We also improved our customer satisfaction levels.
我們也提高了顧客滿意的標準。
助動詞 be 之後：
The reduced consumer demand is also affecting company profits.
消費需求的降低也影響到了公司的利潤。
第一助動詞 have 之後：
I』ve been working in the garden this week, and I』ve also been reading a lot.
這周我在花園裡工作，也讀了很多書。
情態動詞之後：
Our students can also opt to stay in residence.
我們的學生也可以選擇住校。
Also 還可以放在句首，用來強調接下來的或是開啟一個新的話題，例如：
It’s very humid. Also, you can easily get sunburnt.
天氣很潮溼。而且，你很容易被曬傷。
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，我下周給你打電話，到時候再討論。另外，我們需要決定誰將去新加坡。
當 also 置於句末的時候，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.
她在辦公室聯繫了他，但他沒有接電話。他的手機也沒有聲音。
二、as well 在口語中比 also 更常見，而且經常出現在句末，例如：
He should pay and maintain you as well.
他得給你錢，還得供養你。
We should stick to the principles and be flexible as well.
既要有原則性，也要有靈活性。
三、too 通常也放在句末，例如：
Gill’s having chicken. I』ll probably have chicken too.
吉爾在吃雞肉。我可能也要雞肉。
She looks really tired and she must be really hungry too.
她看起來很累，一定也很餓。
當直接指向主語時，too 可以直接跟在主語後面，這時它通常不出現在情態動詞或助動詞後面，而且經常前後用逗號隔開，例如：
I too thought she looked unwell.
我也覺得她看起來不舒服。
We, too, have been very pleased to receive the prize on her behalf.
我們也很高興代表她領獎。
解析：此句不能改成 We have too been very pleased to receive the prize on her behalf.
相比於 also 和 as well，too 更常見於對諸如表達美好願望等固定表達的回應，以及由單個賓語代詞組成的回應，例如：
A: Enjoy the play.
好好欣賞這齣戲。
B: Thanks. You enjoy your evening too.
謝謝。你也喜歡你的夜晚。
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：
Giveme a book of ten first and a book of ten second as well then please.
請先給我一本十歲的書，再給我一本十歲的書。