Explaining the Difference: "By" and "Until"
Both "by" and "until" are prepositions that focus on time. But many students struggle to differentiate between the two and often use one when the other is more appropriate.
This time, we'll dig into some ways we can clearly explain what makes each choice different and when it's best to use one over the other.
By
"By" is used when the focus is on a deadline, a particular point at which something must be done or completed. Therefore, it's always followed by a time or specific event.
I have to finish this project by Friday morning.
They should arrive by 5 p.m.
He should have gotten here by now.
The package should be delivered by the end of the week.
You must complete the test by the time the alarm sounds.
In each of these examples, the end of the period of time is the most important thing.
Until
With "until," however, the end of the period of time isn't the focus; instead it's the complete period of time — the beginning, middle and end.
I have until Friday morning to finish this project.
Here, the speaker is referring to all of the time they have, which starts from now and continues to Friday morning.
It took until 5 for them to arrive.
In this example, the speaker is referencing the complete amount of time that was required for someone to make a journey.
More examples:
The package was in transit until this evening.
How much longer until we arrive?
You have until when the alarm sounds to complete the test.
Until now, I thought "by" and "until" were interchangeable!
In each of these sentences, the total period of time is important — not just the end — so only "until" is correct, not "by."
Yet
Let's finish up with a quick look at one more word that's related to the previous two we've discussed.
"Yet" is similar to "until" because it also refers to a period of time, but the important difference is that the period is not finished.
"Yet" is mostly used in questions and negative sentences, as in the following examples:
Are you finished yet?
Because of some delays, we haven't completed production yet.
We can't start the meeting because the team leader hasn't arrived yet.
Wrap-up
In short, "by" refers to a deadline or endpoint, while "until" focuses on a total period of time. When the period of time isn't complete, "yet" is the best choice.
The explanations we've provided should make the differences between each word easier for your students to grasp. Use the examples above along with your own prompts to test their comprehension until they're comfortable using them all. ⏱️
