在英语的错误中，有两种和标点符号有关。一种是应用逗号却用了句点；另一种应用句点却用了逗号。前种情况使句子不完整；后种情况，则无休止符。
这里就详细谈谈这两个问题。
大家知道，一个完整的句子有主语（The Subject）和谓语（The Predicate）。除了省略句（Elliptical Sentences）之外，一般的句子，都由主语＋谓语组成一个简单句（The Simple Sentence ）。一个短语或分句没有了主句，便是不完整的句子（Fragmentary Sentences），便是错误句。
在下列句子中，①a, ②a, ③a全错；①b, ②b, ③b才对：
①a. I have two purposes of dieting. To save money on food and to trim my waistline.
b. I have two purposes of dieting: to save money on food and to trim my waistline.
②a. That desk has a secret drawer. Into which James stuffed all the old bills.
b. That desk has a secret drawer into which James stuffed all the old bills.
③a. The old men jumped through the window. Because it was the only way of escaping the fire.
b. The old man jumped through the window because it was the only way of escaping the fire.
和不完整的句子呈强烈对照的是只有逗号的句子（Run-on Sentences）。这样的句子，一个接一个，没有句点，也没有连词，这是不对的；因此，④a和⑤a错；④b和⑤b对：
④a. All at once, we knew the answer, Jenny was lying.
b. All at once, we knew the answer. Jenny was lying.
⑤a. Helen is an excellent singer, one of the best in this country, dont you think so?
b. Helen is an excellent singer, one of the best in this country. Dont you think so?
下面这段文字里有些句子不完整，有些又一句接一句，欲罢不能。你能不能把这些错误找出来，并加以改正。
① Tony was a good singer, he went in for singing at a very young age.
② lt goes without saying that he was keen on singing, many people did not like singing at all.
③ But as far as Tony was concerned. Singing became part of his life.
④ Whenever he was tired or ill, he would; as a rule, consider it good to sing a song （for entertainment）.
⑤ The moment Tony played his musical instrument and sang. All living things came to listen to him. In other words, his singing was welcomed by all creatures.
⑥ Like anyone else; Mary loved his singing and decided to marry him.
⑦ Tony too, loved her dearly. At first sight.
⑧ But one day, Mary was killed, in the field.
⑨ For many days Tony was sad at her death. ⑩ Soon he died of grief.
答案：
① a good singer. He went in for
②. singing. Many people
③ concerned, singing
④ he would, as a rule, consider
⑤ and sang, all living things
⑥ Like anyone else, Mary
⑦ loved her dearly at first sight.
⑧ killed in the field
⑨ For many days,
⑩ Soon, he died of grief.