有一次听公开课，内容是：老师讲解“现在完成时的用法”。主讲老师设计了一个单项填空题：
―Where is Tom? I can’t find him.
―_________.
A. He is out B. He was out C. He has been out D. He will be out
可能是疏忽还是什么原因，这位老师选择了答案C. He has been out. 因为是讲解现在完成时的用法，所以，自然是设计并选择与现在完成时有关的选项。可是，问题出来了。
这个题目的正确答案应该是A. He is out. 然而这位老师认为，应该使用现在完成时，强调过去动作或状态对现在的影响。听起来不错，但是，这位老师对He has been out.的理解出现了问题。
我们把这个题目里面所有的选项句子，逐个作一分析：
A. Tom is out. 汤姆出去了，不在家。（指现在的情况）
意味着：Tom is not here now. He may be back in an hour.
B. Tom was out. 汤姆出去了，不在家。（指过去的情况）
意味着：Tom was out when I called at his house.
D. Tom will be out. 汤姆将要外出。（将来时态）
意味着：Tom will go out. Now he is dressing up.
C. Tom has been out. 是什么意思呢？它又两个意思：1.汤姆外出回来了。2.汤姆外出一段时间了（尚未归来）。
如果用He has been out.回答，看起来好像很完美，现在完成时表示对现在的结果或影响，其实不然。因为Tom has been out.属于答非所问，直接用一般现在时Tom is out.即可。那么，Tom has been out.为何会产生这两个意思呢？
这个问题涉及现在完成时的用法问题。下面，我不针对某个具体的句子或现象，而是从规律性的角度总结其用法特征。
1. 一个表动作的终止性动词，其现在完成时（不能与一个时间段连用），表示这个动作发生在过去并已终止。原本使用一般过去时没错，但是，之所以用现在完成时，就是为了强调对现在的影响。例如：
Tom went out.（正确） →Tom has gone out.（正确）
Tom ate an apple. （正确）→Tom has eaten an apple. （正确）
2. 一个表动作的延续性动词，其现在完成时（应该与一个时间段连用），表示这个动作发生在过去并一直持续到说话的时间。因为这个动作是延续的，所以，原则上应该跟一个“时间段”的状语。例如：
Tom has worked in this factory since 1990.
Tom has studied English for ten years. (www.yygrammar.com)
3. 一个表状态的“系表结构”，包括：be +介词短语；be +副词；be +形容词，由于本身具有持续的含义，其现在完成时，跟规则2是一样。又因为这个状态是延续的，所以，原则上应该跟一段时间状语连用。例如：
Tom has been in the office all day. (for ten hours)
Tom has been out since yesterday. (for two days)
Tom has been busy recently. (for a week)
由于2和3的规则一样，所以，可以合并为一项。
在现实语言中，2和3的情况，有时候不带“一段时间的状语”。这下就带来了难题：产生了歧义。歧义有二：
歧义之一：把这个句子理解为省略了已知的时间段状语。例如：
Tom has been out.汤姆外出了（持续至今仍未归）。理解为：
Tom has been out since last night.
Tom has been very busy. 汤姆（近来，最近几天）很忙。理解为：
Tom has been very busy recently (these days).
Tom has been ill. 汤姆（近来）一直病着。理解为：
Tom has been ill recently (for a week).
包括下面3个句子，同样可以理解为省略了已知的时间段状语。
Tom has stayed in the office.（汤姆一直呆在办公室里）
Tom has lived in this town. （汤姆一直住在这座城里）
Tom has been in
(具体省略的时间段状语，略去，不再赘述)
歧义之二：因为没有时间段状语，所以，可以把上述句子理解为这个动作或状态“已经终止或结束”。即上述各句也可理解为：
Tom has been out. 汤姆外出回来了。
Tom has been very busy. 汤姆已忙完了。
Tom has been ill. 汤姆生过病，现在好了。
Tom has stayed in the office. 汤姆曾在办公室里呆过。
Tom has lived in this town. 汤姆在这城里住过。
Tom has been in
【结论】一个持续性的动作或状态，用于“现在完成时”的时候，本来应该带有“时间段”的状语，但有时候却没有，这时，必然会产生歧义。怎么办？只有按照实际语境予以理解和判断！
这些天我一直在思考这个问题。得出以上看法，是经过我深思熟虑，并融入了自己深刻的思辨。
一个持续性的动作或状态，用于“现在完成时”的时候，应该带有“时间段”的状语，这是语言的逻辑，我们应该遵守，否则会引起误解或句子歧义现象。
Tom has been out.这个句子是否符合语法？孤立的一个句子到底是什么意思？
我认为，表动作的go out用现在完成时没错，同样，表状态的be out用现在完成时也没错。问题是，Tom has been out.的含义与Tom has gone out.不同。前者蕴含着“外出一段时间”，后者没有。最关键的问题是，Tom has been out.所表达的意思不清晰。如果回答“Where is Tom?”，我们用“He has gone out.”，或者“He is out.”不用“He has been out.”
我的意思是，并非说have (has) been out一定要跟一个时间段连用，而是说“表状态”的现在完成时，其本身多表示“这个状态持续的时间”。以下例句充分说明了这一点，虽然其中一些have (has) been out表达了比喻的意义，或者含有out of短语，但其本质是一样的。
1. have / has been +out
We have been out on the ice since March and the Arctic summer is nearly here.从三月份到现在我们一直在冰原上，而北极的夏天正日益临近。
A source told the New York Post newspaper: Britney has been missing recent recording sessions because she has been out all night partying.一位消息人士向《纽约邮报》透露：“布兰妮因为整晚忙着派对，所以近来一直没有进棚录音。”
I think it’s important he is back on the field for Manchester United and back playing 90 minutes, and also gets his confidence back because he has been out for a long time.我认为当他康复归来并得能为曼联踢上个90分钟的比赛，这才是重要的地方，这也能让他找回些自信，要知道他可是离开赛场不短的时间了。
It is not headline-making news; this information has been out there for years.这不是故意为了抓人眼球的新闻。这已经多年前就出现的旧闻。
Someone asked me recently if I thought this book was dated, since it has been out for several years. 最近，有人问我是否认为这本书已经过时了，因为这本书从出版到现在已经有好几年时间了。
Some people are saying their service has been out since the morning.有人说从早上起，服务就出问题了。
The coalminers have been out on strike for several weeks now. 煤矿工人已罢工了几个星期。
The fire has been out for hours. 火熄了好几个小时了。
I'm afraid the book has been out for some time. 恐怕这本书已借出一段时间了。
I have been out of shape ever since I left the army.自从我离开军队后，我的身体一直很差。
He has been out of debt since he stopped gambling.他戒赌博后，不再欠债了。
The piano has been out of use for several years.这架钢琴已多年不用了。
Democrats have been out of power for some time.民主党人在野已经有一段时间了。
Many people have been out of work recently.最近有许多人失业。
I have been out of touch with him since last autumn.自去年秋天以来，我就与他失去了联系。
He has been out of condition for several weeks.他身体不好已有几个星期了。
He has been out of touch with his teacher since the war.战争之后，他就和他的老师失去了联系。
The zone is controlled by Russian military forces and has been out of reach during the past weeks due to the unstable security situation.这个缓冲区由俄罗斯军队控制，由于安全形势不稳定，过去几星期来一直无法进入。
这个问题是个例，还是普遍现象？为了有更多的证据佐证这个问题，其他情况“表持续性的动作或状态”的现在完成时，我也找了很多的例句，几乎都是跟一个“表示时间段”的状语连用。
2. have / has been +形容词：
I’ve been busy ever since I came back. 自我回来后一直在忙。
I’m sorry. I've been busy since last month. 对不起，从上个月起就很忙。
He’s been busy with this for quite a few days. 他为了这个忙了好几天。
She has been busy all the day long. 她一整天都在忙。
The Rocket has been busy playing as guest for the last month. 客场作战的火箭队在刚过去的一个月里一直在忙于比赛。
Today I have been busy over your book. 今天我一直忙着看你的书。
These days we have been busy from morning till night. 这些天,我们从早到晚一直在忙。
For the pas two years, I have been busy preparing for the examination. 过去两年来，我一直忙着准备考试。
All these last few days the farmers have been busy fighting drought. 在最后这几天里，农民曾经忙于抗旱。
I have been busy with my science report on sharks for several weeks. 最近几个星期我一直都在忙我的鲨鱼科学报告。
I am very sorry to learn that you have been ill for some time. 听说您最近身体欠佳，心里很不安。
My grandmother has been ill for a week. 我祖母已生病一个星期了。
He has been ill most of the term. 这学期大部分时间他一直生病。
He has been ill for a long time and unable to work. 他患病已久，不能工作。
He has been ill and confined to bed for years. 他多年卧病在床。
Is it for four days that he has been ill? 他生病已有四天了吗?
Her mother has been ill since last Friday. 她妈妈从上周五就有病了。
His grandfather has been ill for a long time. 他爷爷已经病了好久了。
Mum has been ill for nearly a week. 妈妈病了近一周了。
3. have / has been +介词短语：
The roses have been in flower for a week. 这些玫瑰花已经开了一星期了。
Her books have been in popularity recently. 她的书近来大受欢迎。
He is ill and has been in the hospital for a week. 他病了，已住院一星期。
He has been in a spin since the defeat. 他被击败以来一直情绪低落。
She has been in her room for hours. 她在自己的房间里待了几个小时。
Ever since Adam fools have been in the majority. 自亚当以来，一直就是蠢才占多数。
These ideas have been in circulation for some time. 这些想法已经流行了一段时间。
The two political parties have been in conflict since the election. 从大选开始，这两个政党就一直争论不休。
He has been in this class only a few weeks and he is already going ahead. 他来到这个班级才几个星期就已经取得了进步。
She has been in poor health for some time. 她身体欠佳已有些时日了。
The phrase has been in wide use since the 1950s. 这个词组从五十年代起就被广泛运用了。
She has been in the army for three years. 她参军已经三年。
He has been in the business for many years. 他已经商多年。
He has been in the train for a long time. 他坐了很长时间火车
Our party has been in office for three years. 我们的政党已经执政三年了。
4. have / has +延续动词：
She has lived in luxury all her life. 她一生生活奢侈。
He has lived all his life in
He has lived here for the last few years. 过去的几年他一直住在这里。
My family has lived in this village since time immemorial. 我家很早以前就一直住在这个村子里。
He has lived there for a great portion of his life. 他在那里住了大半辈子。
I have stayed in
The temperature has stayed hot this week. 本周气温一直都很热。
I have stayed in this city for ages. 我已经在这个城市呆了许多年了。
He has worked at physics for many years. 他从事于物理研究许多年了。
He has worked in the factory since last year. 从去年开始，他就在工厂里工作。
He has worked for the firm, man and boy, for thirty years. 他从小至今已为该商行干了三十年。
He has worked for us ever since he left school. 他离开学校后一直为我们工作。
The Atlantic cable has worked well for many years. 大西洋海底电缆多年来使用情形良好。
Andrew has worked hard up to now. 安德鲁一直努力工作到现在。
【结论】一个持续性的动作或状态，用于“现在完成时”的时候，应该带有“时间段”的状语，这是语言的逻辑，我们应该遵守，否则会引起误解或句子歧义现象。