2--What does it mean? Let's find out by listening to an American English conversation.
 
1--Hey, what do you want to do this weekend?
 
2--I don't know. We could see a movie or have dinner. Why don't we play it by ear?
 
1--Sure.
 
2--"Play it by ear" means you aren't going to make a firm plan, but will decide what to do as you go along.
 
1--This idiom has a musical meaning too.
 
2--When you don't have the written music for a song, but you play the notes that you think you've heard, you " play it by ear."
 
1--So when you are in a situation where you make a plan as you go, you're " playing it by ear".
 
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注解：
 
1.conversation对话 
2.musical音乐的
3.situation情况 

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译文：
 
1--如果你听美式英语时，你有可能会听到这个短语“Play it by ear（见机行事）”。
2--这是什么意思呢？让我们一起来听听下面的对话吧。
1--嘿，你周末有什么计划么？
2--不知道呀。我们可以看看电影、吃顿饭。到时视情况再定（play it by ear），怎么样？1--好的。
2--“Play it by ear”的意思是你没有一个明确的计划，走一步看一步。
1--在音乐领域，这个俚语也有特定的含义。
2--当你没有一首歌的乐谱时，你是凭借听过的记忆来弹奏这首曲子。你是“凭借自己的耳朵（听过的）来弹奏”（play it by ear）。
1--所以当你处于走一步看一步的情形时，你就是在“即兴弹奏”（引申为：见机行事；play it by ear）。