English usage

Usage is about individual words and phrases; there are no rules or logical explanations for the way they behave - it's just how we happen to say things. For the learner who is looking for patterns in language, this can be frustrating because usage has to be learned case by case.
A first example will help to make this clear. The word often does not seem to be too problematic. The student quickly learns its meaning and that it usually occupies second position in the sentence. For example: I often play tennis on Sundays or My mother often phoned me when I was living in London. But if he tries to follow the pattern and says My mother often phoned me yesterday, he is unfortunately using the word incorrectly. Often can refer to events that are repeated over a longer stretch of time but not to those events that happen in a shorter time period. It has to be My mother phoned me many times yesterday. Similarly, it is incorrect usage to say My car often broke down on the way home if you are referring to one journey - it has to be My car kept breaking down .. or My car broke down several times. It is acceptable, however, if you are referring to all the journeys you made home over a longer period of time. There is no particular reason why often should behave in this way - it is just so.
Now consider the phrases for long and for a long time. These might seem to be synonyms but in fact they have quite different usages and meanings. You can say I waited for a long time but I waited for long is not possible. Conversely, you can say I didn't wait for long but I didn't wait for a long time does not mean the same and is in fact a very unlikely expression. [Its use is just about possible in the following situation: For a long time I didn't wait for the postman to come, but after my grandmother became sick I started to wait anxiously for him every day.]
Question 1
Can you explain the difference in meaning of the following two sentences?
He didn't eat for long.
He didn't eat for a long time.
Now let's look at one or two verb constructions. The words suggest and advise have very similar meanings but their usage is different. We can say both I advise you to go and I advise that you go, but only I suggest that you go is correct; I suggest you to go is not possible. Conversely, I want you to go is right but I want that you go is not.
Question 2
Which constructions using "go" are correct with the verbs allow, defy, command, insist and hope? (For example, are both I insist you to go and I insist that you go correct, only one of them or neither of them?)
There's a similar problem with the synonyms like and enjoy. We can say both I like playing tennis and I like to play tennis but I enjoy playing tennis is correct, whereas I enjoy to play tennis is not. And consider the antonyms stop and start. She started eating is the opposite of She stopped eating, but She started to eat is not the opposite of She stopped to eat.
More on gerunds
Question 3
What does She stopped to eat mean?
Question 4
Which one of the following expressions is incorrect usage?
I don't think she will come
I don't believe she will come
I don't suppose she will come
I don't hope she will come
I don't imagine she will come
Question 5
Look at the following sets of sentences. Which, if any, of the sentences in each set is incorrect usage?
a.
I was written a letter by my grandmother.
I was sent a letter by my grandmother
b.
It cost a lot of money.
It cost a lot of dollars.
c.
It's raining. I know.
It's raining. I know it!
d.
Bye. I'll see you later.
Bye. I'll see you a few days later.
e.
This statue is made of wood.
Paper is made of wood.
f.
Do you want coffee cups or tea ones?
Do you want plastic cups or china ones?
g.
We had a meal together once.
We must have a meal together once
h.
That book is a little interesting.
I feel a little better today.
i.
Is that the new teacher?
I believe. I believe it. I believe so.
j.
Thank you very much. Thanks very much.
Thank you a lot. Thanks a lot.
These are just a few examples of the hundreds of usage problems in the English language. If you want to learn more, I can recommend the following two books:
Practical English Usage, M. Swan (1995) , Oxford University Press
English Usage, Collins Cobuild (1992)

Answers
In most aspects of grammar, we can explain why a particular form is necessary by referring to general patterns. For example, we can say that the indefinite article is needed because it is the first reference to a particular countable object. Similarly, we can justify the use of the present perfect tense becuase we are referring to a completed action that has some connection to the present. There are no explanantions for the answers below, however, since usage deals with the way that individual words or expressions behave. They are how they are, and no patterns or generalities exist to help us predict their behaviour.
Question 1
She didn't eat for long means that she ate for a few minutes and then stopped whereas She didn't eat for a long time means she did not eat, possibly because of illness, for a long period of time and then she started eating again.
Question 2
I allow you to go I allow that you go
I defy you to go I defy that you go
I command you to go I command that you go
I insist you to go I insist that you go
I hope you to go I hope that you go

Question 3
She stopped to eat does not mean the same as She stopped eating; it means she stopped whatever she was doing and started to eat. (For example, she had been walking in the mountains for several hours then she stopped walking in order to eat.)
Question 4
I don't hope she will come is incorrect usage. It has to be: I hope she doesn't come.
Question 5
The following sentences are NOT correct English usage:
I was written a letter by my grandmother.
It cost a lot of dollars.
It's raining. I know it!
Bye. I'll see you a few days later.
Paper is made of wood.
Do you want coffee cups or tea ones?
We must have a meal together once.
That book is a little interesting.
(Is that the new teacher?) I believe. I believe it.
Thank you a lot.