too

Compared meaning: also, in addition (adverb).

比较义项：也，此外（副词，表示追加或补充）。

• also

  Neutral and the most common of the four; usually placed mid-sentence, right before the main verb or after 'be'/an auxiliary; equally natural in speech and writing.

  四词中最中性、最常用；通常放在句中，位于主要动词之前或be动词、助动词之后；口语和书面语都很自然。

  He can play the guitar, and he can also sing well.

  他会弹吉他，也很会唱歌。

• too 本词

  Informal and very common in everyday speech; normally goes at the very end of the clause, not in the middle of it.

  语气随意，日常口语中非常常见；通常放在分句的最末尾，而不是句子中间。

  My sister loves pizza, and I love it too.

  我姐姐喜欢比萨，我也喜欢吃。

• besides

  More formal; often opens the sentence and adds a further point that strengthens what was just said, closer in force to 'furthermore'.

  更正式；常放在句首，用来补充一个能加强前述内容的理由，语气上更接近“此外/而且”。

  Besides being cheaper, the new laptop is also much faster.

  除了更便宜之外，这台新笔记本电脑也快得多。

• likewise

  Formal; signals that a different person or thing does the same kind of action just mentioned, stressing similarity rather than plain addition.

  较为正式；表示另一个人或事物做了与前面所说相同类型的动作，强调的是相似性，而不只是单纯的追加。

  Tom ordered a salad, and his wife likewise chose something light.

  汤姆点了沙拉，他妻子也同样选择了清淡的食物。

All four mean 'also'. Also is neutral and common. Too is informal, used at the end of a clause. Besides is formal, opening a sentence to add a point. Likewise is formal, stressing the same action mentioned. Not covered: too as 'excessive', besides as 'except'.

这几个词在表示“也、此外”这一附加意义时意思相近，但正式程度、语气和句中位置有所不同：also最中性常用，too更口语化且常放在句末，besides更正式，常用来引出补充的理由，likewise强调“同样地做某事”，语气也更正式。这里不比较too表示“过于”的用法，也不比较besides作介词表示“除……之外”的用法。

Compared meaning: more than is needed or proper (adverb).

比较义项：过度、超过应有的程度（副词）。

• too 本词

  The everyday, highly common word for excess; typically followed by 'to' + verb or 'for' + phrase naming the negative result, and natural in both speech and writing.

  表示过度最常用的口语词；后面常接“to+动词”或“for+短语”说明造成的负面结果，口语和书面语都很自然。

  This coffee is too hot to drink right now.

  这杯咖啡现在太烫了，没法喝。

• overly

  More formal and bookish; directly modifies an adjective or participle without needing a following infinitive, and often carries a mildly critical, evaluative tone.

  更正式、更书面化；可以直接修饰形容词或分词，不必接不定式，常带有轻微批评、评价的语气。

  The teacher said the essay was overly long for such a simple topic.

  老师说这篇作文对于这么简单的主题来说写得过长了。

Too and overly both mean more than is needed. Too is the everyday, common word, usually followed by to plus a verb, or for plus a phrase. Overly is more formal and bookish; it modifies an adjective or participle directly and often sounds critical.

too 和 overly 都表示程度超过应有或合适的限度，但 too 是最常用的口语词，overly 更正式、更书面，语气也略带评价色彩；两者在语法搭配上也不同。