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Conquer “not until” with practice exercises with detailed answers

"Not Until" is commonly encountered in both everyday conversation and English proficiency exams like IELTS, and TOEIC. However, people often mistakenly confuse this phrase with Only When. In this article, PREP will help you better understand the definition, usage, and inversions of Not Until.

I. What is “not until”?

What is “not until”? Until is a preposition that indicates time, used to mean "up to the point when". For example:

You’ll have to wait until your next birthday for a new bike.
I will work on my homework until 11 pm.

What is “not until”? “Not until” is often used along with terms or phrases indicating time to emphasize when the action in the following clause occurs. For example:

It was not until 11 pm last night that my brother completed his job.
Not until he faced health issues did he realize the significance of regular exercise.

II. The usage of “not until”

Below are some tips to help you better understand "Not until" in inverted sentences and cleft sentences:

1. Inversion

"Not until" in inversion is often used to emphasize the main clause of the sentence. The structure is as follows:

Not until + time word/clause/phrase + auxiliary + S + (V).

For example:

Not until I finish my work will I join the celebration.
Not until he apologized did she forgive him for his mistake.

2. Cleft sentence

Cleft sentences including "Not until" are often used to express an event that occurred after a specific time. This structure typically consists of two main parts: the subordinate clause (containing "not until") and the main clause (expressing the event that happened after the mentioned time). The structure is as follows:

It (be) + not until + time word/clause/phrase + that + S + (V).

For example:

It was not until I had finished my degree that I found a job in my desired field.
It wasn’t until the sun had set that the temperature began to drop significantly.
It was not until she had read the entire book that she understood its underlying themes and messages.

A cleft sentence with "Not until" expresses the temporal relationship between two events, often used to emphasize the important moment when the following event needs to take place.

III. Only When – An equivalent structure to Not until

At the beginning of this article, PREP has made a note that many students commonly confuse "Not until" with "Only when". How can we distinguish the usage and structure of "Not until" from "Only when"? Let's dive into this matter in the below part!

Criteria		Not until	Only When
Similarities		"Not until" and "Only when" are both English phrases that indicate time, emphasizing the timing of events. These two structures can be used interchangeably with one another in certain contexts, such as rewriting sentences as an exercise. For example: Cathy didn’t start her homework until her mother reminded her. ➞ Only when Cathy’s mother reminded her did she start her homework.
Differences	Usage	"Not until" is used to express an event that occurred after a specific point in time, and up until that time, the event had not yet taken place.	“Only when" is commonly used to indicate a condition that must be met for another event to occur.
	Structure	S + (not V) + O + until + time word/clause/phrase.	Only when + S + (V) + auxilisary verb + S + (V).
	Example	I didn’t realize the truth until he explained it to me. Smith didn’t leave the office until 7 PM.	Only when the rain stops will we go for a walk. Only when she finishes her presentation will she be able to relax.

Note: After "Not until" can be a time word/clause/phrase, however for the structure "Only when", it is MANDATORY to be a clause.

IV. Rewrite sentences with Not until & Only when

Below, some formulas will be provided for rewriting sentence structures combining "Not until" and comparing "Not until" vs "Only when". Students can use these to accurately rewrite different sentence types!

1. Not until

The structures are as follows:

S + (not V) + O + until + time word/clause/phrase.
➞ It is/was + not until + time word/clause/phrase + that + S + (V).
➞ Not until + time word/clause/phrase + auxiliary verb + S + (V).

For example:

He did not understand the complexity of the assignment until the night before it was due.
- ➞ It was not until the night before the assignment was due that he understood the complexity of it.
- ➞ Not until the night before the assignment was due did he understand the complexity of it.
They didn’t realize the importance of saving money until they encountered unexpected financial difficulties.
- ➞ It wasn’t until they encountered unexpected financial difficulties that they realized the importance of saving money.
- ➞ Not until they encountered unexpected financial difficulties did they realize the importance of saving money.

2. Not until & Only when

The structures are as follows:

S + V (negative) + O + until + time.
➞ Only when + clause + auxiliary verb + S + V.

For example:

He didn’t appreciate his parents’ advice until he faced the consequences of his actions. ➞ Only when he faced the consequences of his actions did he appreciate his parents’ advice.
She didn’t leave her house until she felt better. ➞ Only when she felt better did she leave her house.

V. Exercises on Not until, Only when with detailed answers

Below are practice exercises for you to apply the theories you have learned. Try to do them yourself and check the answer below!

Exercise:

1. Not until he finished his work did he take a break.

➞ Only when………………………………………………………

2. She didn’t understand the instructions until the teacher explained them again.

➞Only when……………………………………………………………………………………….

3. Not until they had left the house did they realize they forgot their keys.

➞ Only when…………………………………………………………………………………………………

4. They didn’t start the movie until all the guests had arrived.

➞ Only when…………………………………………………………………………………………….

5. Not until the sun had set did we begin our evening walk.

➞ Only when…………………………………………………………………………………………….

6. Only when the rain stopped did they come out to play.