that连接从句时从句为一个句意完整的陈述句。that不能省略，没有具体的意思，不充当句子成分，只起连接作用。但引导同位语从句的that不能省略
如：The idea that you can do this work well without thinking is quite wrong.
你认为不动脑筋就能做好这件工作的想法是完全错误的。（作idea的同位语）
1.在某些名词（如demand,wish,suggestion,resolution等）后面的同位语从句要用虚拟语气
如：There was a suggestion that Brown should be dropped from the team.
有一项建议是布朗应该离队。
2.引导同位语从句的连词that通常不省略，但在非正式文体中也可以省去。
如：He grabbed his suitcase and gave the impression he was boarding the Tokyo plane.
他拿起了手提箱，给人的印象是他要登上飞往东京的飞机了。
