AS - WHILE - WHEN : difference and use explained

'As', 'when' and 'while' are used to connect two events happening at the same time.
These words mean 'during the time that' or 'at the time that'.
Please note: If a clause starting with 'as', 'while' or 'when' comes before the main clause, a comma is used after it.

AS:
After as, either the simple or continuous form of verbs can be used.

AS: means 'during the time that/at the time that'...:
• As Hugo walked to the door, he put on his jacket.
• Eva picked some flowers as she was walking through the garden.
• Another group of people arrived as we left the museum.
• The girls were sunbathing as the boys were playing volleyball.
• As Emily was getting into the car, she tore her dress.
• All eyes were on the actor as he walked onto the stage.
• As I was driving down the road, I witnessed a strange event.
• She smiled at the waitress as she took the plate.
• The boys were laughing as they left the cinema.

AS: can also mean 'because' or 'since':
• As Tom is taller than you, he should stand behind.
• We'll have to walk up the three floors as there is no other option.
• As I finished my homework, I can go out with my friends.
• I must leave now as I have an appointment.

AS: can also be used to refer to the job, function or role of someone or something:
• Alice works as a part-time receptionist.
• The author is respected as a writer.
• He used a saucer as an ashtray.

WHILE:
While is often used with continuous actions, but not always.

WHILE: meaning 'during the time that/at the time that'.

• Carla came into the room while Tom was watching the match.
• While I was playing the piano, someone knocked on the door.
• A band played in the restaurant while we were having dinner.
• The cat sat beside Alex while he was doing his homework.
• It started to rain while the children were playing in the garden.
• The electricity was cut off while I was baking a cake.

The continuous form is not always used, for example:

• We had a drink while we looked at the menu.
• They had a car accident while they were on a road trip.

WHILE: can also replace 'whereas' in comparisons or for contrast:
• Hugo is intellectual while his brother is athletic.
• While the food was excellent, the service was very poor.

WHEN :
When is more often used to introduce a single completed event:

WHEN: meaning 'at the time that':
• James was walking back home when he heard an explosion.
• Lucy was driving to work when the accident happened.
• When the children arrived home, I was preparing dinner.
• The students stopped making noise when the teacher arrived.
• There was loud applause when he finished his speech.
• When she stood up to address the group, everyone stopped talking.
• My mother was asleep in front of the television when I called to see her.

WHEN: can be used as a conjunction to mean ‘considering that’:
• What's the point in cooking food when nobody is hungry?
• Why bother explaining when the attendees are not listening?
• Try looking for your glasses when you can't see anything without them!

WHEN: is used to ask about the time of an action:
• When are you getting married?
• I don't remember when the decision was made.
• The plumber was asked when he could start the repair work.