Using there is and there are

1. Strange: Look! A big cockroach is there!
   Natural: Look! There's a big cockroach (there)!

2. Strange:I was disappointed to find out that a limit on the number of units a student can take existed.
   Natural: I was disappointed to find out that there was a limit on the number of units a student can take.

3. Strange: Since I became a sophomore, things that I want to do and have to do occurred a lot.
   Natural: Since I became a sophomore, there are many things that I want to do and have to do.

4. Strange: A takoyaki shop was in front of the cram school.
   Natural: There was a takoyaki shop in front of the cram school.

The reason why the first sentences of each pair sound unnatural is that in English, we tend to put new information toward the end of the sentence, after the main verb, in order to emphasize it. We usually put the old information (the information that the listener already knows about or expects to hear about) in the first part of the sentence.

For example, in the sentences in below (a) and (b), the old information is italics and the new information is in bold type.

In a self-introduction:

1. Hello, my name is Vicky.
2. I'm from the U.S., and I've been living in Japan for three years.

The italicized words are old information in the sense that these are the usual topics found in a self-introduction. The information in bold type is new information that the listener doesn't yet know and can't predict.

The sentences in (i) and (ii) below describe the same basic facts as those in above, but the information appears in a different order. These sentences are grammatical but they would sound very unnatural in a self-introduction.

1. Vicky is my name.
2. The U.S. is where I come from and Japan is where I have been living.

Here, my name, where I am from and where I live are emphasized as new information, while Vicky, the U.S. and Japan are old information. It's hard to imagine a context in which someone would use these sentence. Probably, we would only use them to correct someone's mistakes: 'Vicky is my name, not my hometown, and the U.S. is where I am from, not where I plan to study.'

(Notice that in Japanese, the old information is often optional and can be ommitted. �iڳ�����O��j��B�L����B)

Many times, Japanese students write English sentences which are grammatical but which sound strange because the old information and new information are not where we expect them to be. In the sentence in (1) above, for example, the focus is on a big cockroach, so it is better to put this phrase after the main verb. Likewise, in (4), the writer ouuting the focus on the fact that a takoyaki shop exists, so a takoyaki shop should come after the main verb. Using there is is a good way to do this.

There is also used in negative sentences when we want to talk about the fact that something does not exist, as in the following examples.

1. Strange: In Japan, the debate over this issue has not been held much
   Natural: In Japan, there has not been much debate over this issue.

2. Strange: Without solving this problem, no debate can be done.
   Natural: Until we solve this problem, there can be no debate.

There's a useful reference book for helping you to understand the differences between the English and the Japanese ways of expressing ideas in sentences: Situation vs. Person Focus; ��{Ԑ�����ҭ��pԐ������ by John Hinds, published by �Э������o�.