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Since的用法 Since分别有两种含义：时间和原因。我们可以依照句子句意、结构和时态，决定since在句子中的意思。 1. 时间 在时间的层面上，与「自从」有相似的意思。 Since通常可作为介系词代入一个片语、或连接词代入一个子句、或是以副词单独存在。另外，since后的子句大多是过去式，主要子句为完成式。 连接词 当since用作连接词时，可搭配一段期间或某个时刻，引导时间附属子句，意为「自从…」。附属子句，即 since 子句，的动词通常为过去简单式或现在完成式，而主要子句则使用现在完成式或过去完成式，但以现在完成式居多。如要表示一段期间，since子句该为现在完成式；如要表示某个时刻，since子句便为过去简单式。不论是过去简单式还是现在完成式，意思大致上相同。 【例】I haven’t done any outdoor activities since I graduated from university. 【例】John had been cooking his own dinner since he was twelve years old. 在另一种情况下，当主要子句的结构为” It + be + 时间 + since”，可以以四种不同的句型构成，但意思绝对相同。主要子句的be以现在简单式 is或现在完成式 has been，而附属子句则为过去简单式或现在完成式。在美式英语中，” It has been… since…” 比较常见。 【例】It is ten months since Paul and Linda moved to a new apartment. 【例】It is ten months since Paul and Linda have moved to a new apartment. 【例】It has been ten months since Paul and Linda moved to a new apartment. 【例】It has been ten months since Paul and Linda have moved to a new apartment. 其实在刚刚说明的结构中，be亦可使用过去简单式 was 或过去完成式 had been，但此时 since 子句须使用过去简单式或过去完成式。 【例】It was ten months since Paul and Linda moved to a new apartment. 【例】It had been ten months since Paul and Linda had moved to a new apartment. 当 since 不是引导过去某个动作或事件，而是过去的某个状态并现在一直持续着 ，主要子句及其附属子句都要用现在完成式。 【例】Tom has been sleeping less than 4 hours every day since he has become a doctor. 副词 作为时间副词，since/since then有着「此后，从此，自那以后」的意思。 而ever since能用来加强since和since then的语气。 【例】We graduated from secondary school a year ago and we haven’t reunited since/since then. 【例】They divorced a few months ago and haven’t contacted each other ever since. 介系词 作为介系词时，since只能与某一时刻搭配，即是since之后必须接着日期、年份等时间有关的词。时刻能以副词（e.g. yesterday）、名词片语（e.g. the beginning of the match）或动作动词（e.g. I left）表示。意为「自从…，自…以来，从…至今」。 【例】Since yesterday, I haven’t eaten anything. 【例】Since the beginning of the match, she has been cheering loudly for her teammates. 【例】Since I left my previous workplace, it has become much quieter than before. 在某种情况下，我们可以将since从连接词变成介系词—就是当 since 子句和主要子句的主词（subject）是相同时，便可省略 since 子句的主词。这样，本身句中的主动词须改为动名词 ，接在since后。 【例】Since attending tutorial classes, I have become more confident when answering questions during lessons. （原句：Since I have attended tutorial classes, I have become more confident when answering questions during lessons.） 2. 原因 除了在时间方面，since 亦可作为连接词，引导表示原因的附属子句，意为「既然」。 Since接着的子句通常是现在式，亦能是整个前后子句都为过去简单式。放在主要句子前或后都同样没问题。 Since的运用大多想表达显而易见或已成事实的原因。 【例】Since it is too cold out there, I will just stay home today. 【例】Since the power is out, we should just go to bed directly. 其他词能取代since吗？ 1. Since vs. For Since和for同为时间介系词，适用于完成式的句子，表达某人已做了某件事或处于某个状况一段持续的时间。可是，它们的用法有些不同，所以for是不能替代since。接着，让我们看看应如何区分since和for。 Since + 特定时间点（point of time）：表示当事件发生在某个时刻时 【例】She has lived with her husband since she got married. 【例】I have stopped drinking milk since three years old. For + 时间长度（length of time）：表示当事件持续了一段时间 【例】She has lived with her husband for five years. 【例】I have stopped drinking milk for ten years. 2. Since, Because, As Since，because 和as都可写作「因为」，用法大致上相同。唯一少许的差异在于它们的语气。 Because的语气最强，其次是since，as算是最温和。 Since及as用作对已知的事实提供理由和原因，并非表示直接原因，视附属子句（since/as子句）为附加资料。还有，通常since和as的子句会加上逗号，将原因和主要子句分开，降低原因的重要性。 Since的语气比as稍微强一点和正式一点。 Because则是表示直接原因，强调原因。适合用于回答why的问题，以及引导从句。 |
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