for certainとcertainly、他

質問

I was sent to have my eyes tested. He took me into the darkened interior and said, "Sit down, dear." He put his arm round my shoulder. His forefinger moved up and down on my neck. I was thirteen and didn't like to be rude to him. Dorothy Simmonds, his sister, came downstairs just then; she came upon us silently and dressed in a white overall. Before she had crossed the room to switch on a dim light Mr Simmonds removed his arm from my shoulder with such a jerk that I knew for certain he had not placed it there in innocence.

Muriel SparkのThe Dark Glassesからの英文です。

Mr Simmonds removed his arm from my shoulder with such a jerk that I knew for certain he had not placed it there in innocence.のところはsuch~that構文だと思うのですが、

●a jerkはどのように意味をとるとよいですか？

●for certainとcertainlyは同じ意味ですか？
使い方に何か違いはあるのでしょうか？

前文は

At the end of the thirties Leesden End was an L-shaped town. Our house stood near the top of the L. At the other extreme was the market. Mr Simmonds, the oculist, had his shop on the horizontal leg, and he lived there above the shop with his mother and sister. All the other shops in the row were attached to each other, but Mr Simmonds' stood apart, like a real house, with a lane on either side.

となっています。

教えてください。
宜しくお願いします。

回答No.1

Oubli · ベストアンサー

jerkは「急にはじまる動作」を表します。妹が電灯を点けようとしたら「急に彼の腕を私の肩から離した」ので、明るいところではまずい、何か良からぬことをしようとしていたことが解った、ということでしょう。

for certainとcertainlyは副詞（句）で、意味は大体同じです。ちょっとニュアンスに違いがあるようにも思いますが私には説明できません。ただし、for certainはThat's for certain.のように形容詞句的にも使いますが、こちらはcertainlyでは代用できません。

お礼

jerkとfor certainとcertainlyについて教えてくださってありがとうございます！
jerkは「急にはじまる動作」ということと合わせてご解説も頂いて、よくわかりました。
for certainとcertainlyの用法について教えて頂いてありがとうございました。