这四个词都可表示“也”,但其用法有所不同:
also用于肯定句,常放在句中,位于系动词或助动词之后,谓语动词之前。如:
John also plays the piano.约翰也弹钢琴。
His wife went abroad last year and he will also go abroad.他妻子去年出国,他也要出国。
as well用于肯定句,一般放在句末。如:
He speaks French,and English as well.他既能说法语,也能说英语。
too和as well一样,用于肯定句中,一般放在句末,但too可以紧接在主语后面,在“简略答语”里用于宾格代词之后。如:
I,too,will help you.我也要帮助你。
—I want to eat an apple.我想吃个苹果。
—Me too.我也想吃。
either用于否定句中,一般放在句末,肯定句变否定句时,其中的also和too等要改成either。如:
I don't watch TV,either.我也没看电视。
He won't go,either.他也不会去。