since有没有如果的意思

【since没有如果的意思。】
Since用法
一．Since作为介词，后接某一确定的时间点，主句谓语动词是持续性动词，常与现在完成时态、现在完成进行时态或过去完成时态连用。例如：
1、He left the village in 1982 and I haven’t seen him since then.1982年他离开这个村子，从那以后我再没见过他。
2、She’s been working in a bank since leaving school.她中学毕业后就一直在一家银行工作。
3.He had spoken to her only once since the party. 自从那次聚会以来，他只跟她说过一次话。
二．Since作为副词，表示从过去以来、以后或到现在的情形或状态，常与现在完成时态连用。例如：
1．He left home two weeks ago and we haven’t heard from him since. 他两周前离开了家，到现在我们一直没有他的消息。
2．He came to Zhenjiang 6 years ago and has lived here (ever) since.他6年前来到镇江，从此便住在这里。
三．since引导原因状语从句
作为连词，since可引导原因状语从句，表示因为；既然；鉴于：例如：
1． He didn’t come since he was busy.他因为忙，所以没有来。
2． Since this method doesn’t work,let’s try anoter.既然这种方法不行，我们就试用另一种吧。
四．Since引导时间状语从句
1．若since引导的状语从句的谓语是终止性动词的过去时，则从句表示的时间是“从动作开始的那一时刻起”。例如：
He has studied very hard since he came to our school.自从他来到我们学校，他学习就非常努力。
We have been missing them since they left here自从他们离开这里，我们就一直很想念他们。
2．若since引导的状语从句的谓语动词是持续性动词或表示状态动词的过去时时，则从句表示的时间是“从动作或状态结束时算起”。例如：
I haven’t heard any noise since I slept. Sleep 为持续性动词，sleep的动作结束时，即“醒来”时，所以这句应译为“我醒后还未听到任何声音”。
3．若since引导的状语从句的谓语为持续性动词的现在完成时，则表示动作和状态延续到现在（说话时刻），其表示的时间的起点应从动作发生之时算起。
例如：I haven’t heard from him since he has lived there。 这里has lived表示动作的持续性，时间的起点应从：“开始居住”时算起。因此此句可理解为“自从他（开始）住在那儿起，我就一直没收到他的来信”。
五．Since在特殊句型中的应用
句型I：“It is （has been）+时间+since+持续性动词的过去时”，表示“自从……以来到现在已有多久。”例如：
It has been quite some time since I was last in London.我上次离开伦敦至今颇有一段时间了。
句型II：“It was+时间+since+持续性动词的过去完成时”,表示“从……到过去某时间点以来”，例如：It was three years since we had been here.那时我们在这已呆了三年。

有没有如果的意思
SINCE
1. conjunction (TIME) 时间 /sɪnts/
from a particular time in the past until a later time, or until now 自从…；从…以来
I've been very busy since I came back from holiday. 我度完假回来后就一直很忙。

2. conjunction (BECAUSE) 因为 /sɪnts/
because; as 因为；既然
Since we've got a few minutes to wait for the train, let's have a cup ofcoffee.
既然等火车还需要几分钟，我们去喝杯咖啡吧。
.
3. adverb
from a particular time in the past until a later time, or until now 此后，从此
Emma went to work in New York a year ago, and we haven't seen her since.
埃玛一年前去纽约工作了，自那时起我们就没有见过她。
He started working for the company when he left school, and has been there ever since (= and is still there). 他毕业后就开始为这家公司工作，在此之后他一直呆在那里。
I've long since (= long ago) forgotten any Latin I ever learned.
我早就把我学过的那点拉丁语忘光了。

4. preposition
from a particular time in the past until a later time, or until now 自从…；从…以来
England have not won the World Cup in football since 1966.
1966年以后，英格兰队就再没有拿过世界杯冠军。
It was the hottest October since records began. 这是有史以来最热的十月。