my mind wasn't on what he was saying.为什么不能用had said,时态一致是什么意思?

你好. 语法对的,但意思不一样.
1 My mind was on what he had said ------当时我在想他以前说的话.
2 My mind was on what he was saying-----当时我在想他正在说的话.

时态一致指的是,比如说：
1 He is a doctor and has worked in this hospital for 10 years.(is和has都是指现在,时态是一致的)
2 He is a doctor and had worked in this hospital for 10 years.( 在这里,is与had就不一致了.)如果要保持时态的一致,就必须是：He is a doctor and has worked in this hospital for 10 years. 或者是He wasa doctor and had worked in this hospital for 10 years.(现在完成时和过去进行时算一致吗？不一致。------ I was thinking about what he has said.--------不一致 I was thinking about what he had said -------一致的。