反身代词前什么时候用by什么时候不用by

反身代词的用法：
1、 反身代词不能作主语，但是它可以作主语同位语，放在主语后或句末。:如：我亲自去了电影院。误：Myself went to the cinema.正：I went to the cinema myself.

2、 反身代词可以作宾语的同位语。如：I wish I could hear Beethoven himself play this music.我希望我能听贝多芬他亲自弹这首曲子。You can go and ask him himself.你可以去问他本人。

3、 反身代词可以作介词的宾语。如：Nobody, she learnt it all by herself.没人，她自学的。I mended the bike by myself.我独自修的自行车。She said to herself: ”what’s wrong with my eyes?”她自言自语地说，“我的眼睛怎么啦？”Don’t always think of yourself.别总是想着你自己。

4、 反身代词作动词的宾语。一般放在像这样的动词的后面：enjoy, help, hurt, teach, wash, look after, get dressed, buy等。如：Did you enjoy yourselves at the weekend? 你们周末玩得开心吗？He teaches himself English at home.他在家自学英语. “Help yourselves to some fish .children。”“ 孩子们，随便吃一些鱼 。” He can buy himself a lot of nice things.他可以给自己买好多好东西。

5、反身代词可以作表语。如：I’m not quite myself today.我今天情绪不好。He doesn’t seem himself this morning.今天上午他似乎不舒服。

例如
i myself am a clergy 不要

i did it by myself 要