The following are all positive sentences:
1. I will think about it.
2. Timothy has called her.
3. The teacher was listening.
Can you turn them into negative sentences, using the word not? The related negative sentences are:
4. I will not think about it.
5. Timothy has not called her.
6. The teacher was not listening.
(Of course, native speakers often put not in contractions, saying, for example, I won't think about it instead of I will not think about it; we will not be focusing on the contractions in our discussion here.)
No native speaker of English would make the negative sentence something like, *I will think about not it. That's because there's a systematic relationship between positive and negative sentences, even though they don't have the same meaning. We're not usually consciously thinking about how to make a sentence negative, but we know how to do it, and we do it in a consistent way.
Can you figure out exactly where you put not in a sentence when you make it negative?
Here are some negative sentences, with not underlined and the helping verb in bold. (See Lesson 31 for a reminder about helping verbs.)