Prepositions are often small words, but they are hugely significant, which is why sometimes they can cause huge problems. A sailor’s wife was once told that her husband’s ship was ‘˜in the sea’. She fainted. She thought the ship had sunk. What the speaker had really meant was that the ship was ‘˜on the sea’.
It is the correct use of prepositions that frequently separates a good speaker from a bad one, and a good writer from his poor counterpart. The trouble is that English prepositions are used in such a variety of ways that the rules of their usage are sometimes difficult to pin down. The secret is to practice, practice, and practice ‘“ a time comes when you just pick up the correct word by instinct.
What is the difference between having something ‘˜in your mind’, and having something ‘˜on your mind’? Most informed people will tell you that you have something ‘˜on your mind’ when you are worried, as in ‘œNow that he’s lost the elections, he’s got a lot on his mind’, and that you have something ‘˜in your mind’ when you are simply thinking about something. But hold it! When Facebook asks you, ‘œWhat’s on your mind?’ it is certainly not asking you what you are worried about. So, sometimes you just have to use your common sense to arrive at what the intended meaning is.
While it would be impossible to cover each and every context in which the prepositions ‘˜in’ and ‘˜on’ are used, here are some of their more common uses:
In is used:
‘¢ To refer to the time in which something happens:
He was born in 1999.
They married in September.
‘¢ To refer to a place within a particular area or volume:
They live in a big city in China.
There are many islands in the Indian Ocean.
‘¢ To refer to the way someone is dressed:
The lady was dressed in red.
The police officer was in full uniform.
‘¢ To indicate movement into something:
Put this note in your pocket.
He dipped his hand in the water.
‘¢ To refer to an activity that occurs within a specified period of time:
I’ll be with you in a moment.
She’ll return in a month’s time.
‘¢ To refer to the condition of something or someone:
This room is in a real mess.
Why are you in such a hurry?
‘¢ In the sense of ‘˜regarding’ or ‘˜with reference to’:
He might be weak in English, but he is excellent in Mathematics.
This food is rich in protein.
‘¢ To refer to how something is arranged:
This book has been written in two parts.
The children are sitting in rows.
‘¢ To indicate an activity or occupation:
David is in the army.
He wastes a lot of money in gambling.
‘¢ In the sense of ‘˜contained within’:
There are 365 days in a year.
There are four apples in this bag.
On is used:
‘¢ To refer to the surface of something:
Put that book on the table.
There are ink stains on the floor.
‘¢ To refer to particular day:
She is going home on the 15th of this month.
We celebrate his birthday on the 10th of May.
‘¢ To refer to something a person carries:
Do you have a pen on you?
He has got a jacket on.
‘¢ To refer to an action or state:
She went to Montreal on business.
The house is on sale.
‘¢ To mean ‘˜concerning’:
He is an authority on air pollution.
She delivered a speech on the refugee problem.
‘¢ To refer to the taking of a drug or medicine:
She is on insulin these days.
The patient is presently on anaesthesia.
‘¢ In connection with the part of a body:
He kissed her on the cheek.
He was struck on the head.
‘¢ To indicate that someone is engaged in a particular activity:
He is on a garbage-cleaning mission.
The President is on a tour of the United States.
‘¢ To refer to membership in a body:
Mr. Davis is on the sports committee.
She is on the jury.
‘¢ In connection with the use of a mechanical device:
The program will be shown on television.
Right now, he is working on the computer.
As in the case with ‘˜in’ and ‘˜on’, prepositions acquire meaning only when they are combined with other words or phrases.