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主题句通常以判断句的形式出现，在文章中的通常位置为第一段首句、第一段末句和全文末句等地方。
(1)主题句在首段首句
许多文章开门见山，一开始就摆出要说明的主要对象或要论述的主要观点，接下去的句子和段落都说明或论述它。这样，文章的结构就属于从一般到具体，主题也就在首段首句。例4
Researchers have established that when people are mentally engaged, biochemical changes occur in the brain that allow it to act more effectively in cognitive(认知的)ar-eas such as attention and memory. This is true regardless of age.
People will be alert(警觉的)and receptive(愿意接受的)if they are faced with information that gets them to think about things they are interested in. And someone with a history of doing more rather than less will go into old age more cognitively sound than someone who has not had an active mind.
Many experts are so convinced of the benefits of challenging the brain that they are putting the theory to work in their own lives. "The idea is not necessary to learn to memorize enormous amounts of information,"says James Fozard, associate director of the National Institute on Aging. "Most of us don't need that kind of skill. Such specif- ic training is of less interest than being able to maintain mental alertness. " Fozard and others say they challenge their brains with different mental skills, both because they enjoy them and because they are sure that their range of activities will help the way their brains work.
Gene Cohen, acting director of the same institute, suggests that people in their old age should engage in mental and physical activities individually as well as in groups. Cohen says that we are frequently advised to keep physically active as we age, but older people need to keep mentally active as well. Those who do are more likely to maintain their intellectual abilities and to be generally happier and better adjusted, "The point is, you need to do both," Cohen says. "Intellectual activity actually influ-ences brain-cell health and size. "
本文以引经据典的方法强调了头脑健康，尤其是老年人头脑健康的重要性。这个中心内容在第一段第一句就已指出：人在用脑时，大脑会处于兴奋状态，这时大脑在诸如注意力和记忆力等属于认知领域的能力方面会得到有效发挥。
What is the passage mainly about?
A. How biochemical changes occur in the human brain.
B. Why people should keep active not only physically but also mentally.
C. How intellectual activities influence brain-cell health.
D. Why people should receive special mental training as they age.
这道题的正确答案为B。A与C均为原文中的细节，而D与原文第三段第4～5行“…Such specific training is of less interest than being able to maintain mental alert-ness”相矛盾，所以都不是正确答案。
(2)主题句在第一段末句
首段末句也是主题句常出现的地方。假若如此，这个主题句就不仅是对全文的总结，也是对第一段的总结，而且开启第二段及以后的说明或论述。简而言之，这种文章结构是：具体说明或论述(一段)一总结(一段末的主题句)一后文的具体说明或论述。这种形式的主题句之前通常有表示总结的提示词，如：in conclusion，to conclude， in summary，to sum up，in short，in brief，in a nutshell;或表示推断的提示词：there-fore，thus，as a result，accordingly;或表示转折的提示词：but，however等。转折之后就出现主题句的情况较多，这种谋篇套路可以用“去旧取新、标新立异”八个字概括。文章中诸如“every parent”、“a popular belief”、“frequently assumed”、“universally accept-ed”等词句提示作者可能在下文提出一个与之不同的观点标新立异，假若如此，那么作者“标新立异”之处的观点就是主题大意。对于某一现象，过去已有解释，作者提出新的解释，新解释就是主题大意。这体现了上述的“去旧取新”原则。
例5
Do you find getting up in the morning so difficult that it's painful? This might be called laziness, but Dr. Kleitman has a new explanation. He has proved that everyone has a daily energy cycle.
During the hours when you labour through your work you may say that you're 'hot’. That's true. The time of day when you feel most energetic is when your cycle of body temperature is at its peak. For some people the peak comes during the fore- noon. For others it comes in the afternoon or evening. No one has discovered why this is so, but it leads to such familiar monologues(自言自语)as: 'Get up, John! You'll be late for work again! ’ The possible explanation to the trouble is that John is at his temperature-and-energy peak in the evening. Much family quarrelling ends when hus- bands and wives realize what these energy cycles mean, and which cycle each member of the family has.
You can't change your energy cycle, but you can learn to make your life fit it bet- ter. Habit can help. Dr. Kleitman believes. Maybe you're sleepy in the evening but feel you must stay up late anyway. Counteract(对抗)your cycle to some extent by ha- bitually staying up later than you want to. If your energy is low in the morning but you have an important job to do early in the day, rise before your usual hour. This won't change your cycle, but you'll get up steam and work better at your low point.
Get off to a slow start which saves your energy. Get up with a leisurely yawn(呵欠)and stretch. Sit on the edge of the bed a minute before putting your feet on the floor. Avoid the troublesome search for clean elothes by laying them out the night be-fore. Whenever possible, do routine work in the afternoon and save tasks requiring more energy or concentration for your sharper hours.
If a person finds getting up early a problem, most probably
A. he is a lazy person
B. he refuses to follow his own energy cyde
C. he is not sure when his energy is how
D. he is at his peak in the afternoon or evening.
这段文章先提出现象：早晨起床困难，接着以不肯定的口吻提出一种解释，然后“but”一转，提出Kleitman博士的新解释：各人的精力在一天之中有个周期。这个“but”之后的新解释就是主题句。
(3)文章首末两段均有主题句
主题句到末段才出现的情况较少，常见的情况是文章开门见山提出主题句，中间加以论述，文末复述首段的主题，这也是写作方法之一。例6
Attention to detail is something everyone can and should do -- especially in a tight job market. Bob Crossley, a human-resources expert notices this in the job applica- tions that come across his desk every day. "It's amazing how many candidates elimi- nate themselves," he says.
"Resumes(简历)arrive with stains. Some candidates don't bother to spell the company's name correctly. Once I see a mistake, I eliminate the candidate,"Crossley concludes. "if they cannot take care of these details, why should we trust them with a job?"
Can we pay too much attention to details? Absolutely. Perfectionists struggle over little things at the cost o{ something larger they work toward. "To keep from los- ing the forest for the trees, "says Charles Garfield, associate professor at the Universi- ty of California, San Francisco, "We must constantly ask ourselves how the details we're working on fit into the larger picture. If they don't, we should drop them and move to something else. "
Garfield compares this process to his work as a computer scientist at NASA. "The Apollo Ⅱ moon launch was slightly off-course 90 percent of the time,"says Garfield. "But a successful landing was still likely because we knew the exact coordinates of our goal. This allowed us to make adjustments as necessary. "Knowing where we want to go helps us judge the importance of every task we undertake. Too often we believe what accounts for others' success is some special secret or a lucky break(机遇). But rarely is success so mysterious. Again and again, we see that by doing little things within our grasp well, large rewards follow.
Which of the following is the author's advice to the reader?
A. Although too much attention to details may be costly, they should not be overlooked.
B. Don't forget details when drawing pictures.
C. Be aware of the importance of a task before undertaking it.
D. Careless applicants are not to be trusted.
题干问作者对读者的建议，其实就是问文章的主题。本文开头提出要成就一番大事业，必须从小事做起。中间几段分别从使用沾满墨迹的求职履历表遭淘汰、小事与大事的辩证关系及其例证两个方面论证主题。文章最后呼应文章开头的主题：任何人取得成功都是靠一点一滴做出来的，成功的秘密只有一条：千里之行，始于足下。因此A为正确答案，而B、C、D均无法由文章本身推出，为错误答案。
(4)主题句在文章中间
主题句出现在文章中间的情况也有，而且通常在第二段。倘若如此，文章的逻辑结构通常属于下面两种中的一种。a.从现象(或问题)到主题，再阐述或论证;
b.从一个观点(旧观点或大众观点，即作者要驳斥的观点)到主题(新观点，即作者观点)，再阐述或论证。属于这种逻辑结构的，往往伴有表示转折的提示词，如but，how-ever等。
例7
For some time past it has been widely accepted that babies--and other creatures-- learn to do things because certain acts lead to "rewards”; and there is no reason to doubt that this is true. But it used also to be widely believed that effective rewards, at least in the early stages, had to be directly related to such basic physiological(生理的)"drives" as thirst or hunger. In other words, a baby would learn if he got food or drink or some sort of physical comfort, not otherwise.
It is now clear that this is not so. Babies will learn to behave in ways that produce results in the world with no reward except the successful outcome.
Papousek began his studies by using milk in the normal way to "reward" the ba- bies and so teach them to carry out some simple movements, such as turning the head to one side or the other. Then he noticed that a baby who had had enough to drink would refuse the milk but would still go on making the learned response with clear signs of pleasure. So he began to study the children's responses in situations where no milk was provided. He quickly found that children as young as four months would learn to turn their heads to right or left if the movement "switched on" a display of lights--and indeed that they were capable of learning quite complex turns to bring about this result, for instance, two left or two right, or even to make as many as three turns to one side.
Papousek's light display was placed directly in front of the babies and he made the interesting observation that sometimes they would not turn back to watch the lights closely although they would"smile and bubble" when the display came on. Papousek concluded that it was not primarily the sight of the lights which pleased them, it was the success they were achieving in solving the problem, in mastering the skill, and that there exists a fundamental human urge to make sense of the world and bring it un-der intentional control.
Papousek noticed in his studies that a baby
A. would make learned responses when it saw the milk
B. would carry out learned movements when it had enough to drink
C. would continue the simple movements without being given milk
D. would turn its head to right or left when it had enough to drink
这篇文章开始指出人们以往接受的一种观点(老观点)：婴儿(其他生物也是一样)学做某些事(动作)，是因为做这些事(动作)可以得到“奖赏”;随后进一步指出，过去人们普遍认为(老观点)：这种“产生预期效果的奖赏”都和满足诸如口渴、饥饿等关于人的 “基本生理需要”直接相关。
在第二段一开始，作者指出(新观点)：情况并非如此。婴儿学做某种动作，是想让这些动作在周围世界产生结果，而不是为了得到单纯满足生理需要的“奖赏”。
第三段和第四段讨论Papousek的实验，并得出结论：人类自身存在着一种内在的了解世界并力图对其有意识地加以控制的欲望。
由上可知，本文的结构属于从旧观点到主题(新观点)，再论证。主题句为第二段的第二句话。
