一、從詞性上看區(qū)別

first可用作形容詞或副詞，有時(shí)還可用作代詞;而at first作為介詞短語(yǔ)，只起副詞用作用(在句中用作狀語(yǔ))。如：

First class is the most expensive way to travel. 坐頭等艙是最貴的旅行方式。(first為形容詞，在句中用作定語(yǔ))

This is the first time I have heard of such things. 這是我第一次聽(tīng)到這樣的事。(first為形容詞，在句中用作定語(yǔ))

You needn’t read the whole book hut you must read the first four chapters.你們不必把整本書(shū)全讀完，但必須讀完前四章。(first為形容詞，在句中用作定語(yǔ))

I asked them to ring first in case we were out. 我請(qǐng)他們先打電話來(lái)，以防我們不在家。(first為副詞，在句中用作狀語(yǔ))

She’s always the first to arrive and the last to leave. 她總是第一個(gè)來(lái)，最后一個(gè)離開(kāi)。(first為代詞，可視為其后省略了one, person等之類(lèi)的詞)

His second suggestion was not much better than his first. 他的第二個(gè)建議比第一個(gè)好不了多少。(first為代詞，可視為其后省略了suggestion)

At first we used hand tools. Later we had machines. 開(kāi)始我們用手工工具，后來(lái)我們有了機(jī)器。(at first在此用作狀語(yǔ))

二、從用法上看區(qū)別

1. first的用法

first 用來(lái)說(shuō)明順序，意為“先……”，暗示接下去還有其他動(dòng)作或事件要發(fā)生，因此其后往往接有(或暗示有) then, next, last 等詞。如：

Think first, then act. 先想清楚再行動(dòng)。

I’ll have to finish my homework first. 我得先把作業(yè)做完。

First (you) boil some water. Then (you) warm the teapot. Then (you) add three teaspoons of tea. Next, (you) pour on boiling water... 你先燒些開(kāi)水，然后把茶壺燙熱，接著放三勺茶葉，隨后沖入開(kāi)水……

John came home from work. First he read the paper for a while, then he got up from the chair and turned on the radio. 約翰下班回家，先看一會(huì)兒報(bào)，然后從椅子上站起來(lái)，打開(kāi)收音機(jī)。

2. at first 的用法

at first 的意思是“起初”“開(kāi)始”，它主要用于強(qiáng)調(diào)前后對(duì)照，暗示接下去的動(dòng)作與前面的動(dòng)作不同甚至相反，因此常有 but, afterwards, soon, at last 等相呼應(yīng)。如：

At first I didn’t want to go, but I soon changed my mind. 我開(kāi)始不想去，但我很快就改變了主意。

The work was hard at first, but I got used to it. 起初這活兒很累，不過(guò)后來(lái)我習(xí)慣了。

At first they were very happy, but then things started going wrong. 起初他們生活得很幸福，但后來(lái)就開(kāi)始出問(wèn)題了。

At first I paid little attention, but slowly my interest awoke. 起初我沒(méi)怎么注意，但逐漸產(chǎn)生了興趣。

三、其他幾點(diǎn)區(qū)別

1. at first 除以上用法外，其他場(chǎng)合一般不用它;而first除表示“先……(然后……)”外，還可表示“最先”“第一次”“首先”等。如：

Ladies first. 女士?jī)?yōu)先。

That’s mine—I saw it first. 那是我的，是我先看見(jiàn)的。

When did you first meet him? 你第一次見(jiàn)他是什么時(shí)候?

2. 有時(shí)at first并非固定搭配(first后還修飾有其他詞語(yǔ))。如：

She was so nice a girl that he fell in love with her at first sight. 她是這樣好的一個(gè)姑娘，使他一見(jiàn)鐘情。

She could tell at first glance to which class a man belonged. 她一眼就能看出一個(gè)人屬于哪個(gè)階級(jí)。

3. at first與at last不是一對(duì)反義詞組，后者的意思是“終于”“最終”。如：

At last the truth became known. 最后真相大白了。

She has at last got everything ready. 她最后把一切準(zhǔn)備好了。

At last the bus came. I had been waiting for half an hour. 最后公共汽車(chē)來(lái)了，我已等了半小時(shí)。