At once

At once

“At once” has two meanings, and they’re very different. To make things even more complicated, neither meaning really has anything to do with the word “once,” which means “just one time.”

Here are the two ways to use “at once.” First, it can mean, to do something immediately, without delay, without waiting at all. If a child is misbehaving, you might scold her and say, “Stop doing that at once!” It means, stop doing that right now.

The second way to use “at once” is to do multiple things at the same time. Have you made a big mistake at work? Maybe you were trying to do too many things at once. Maybe you were trying to do too many things at the same time.

Let’s take a deeper dive into the two meanings.

Do something immediately

The first meaning is to do something immediately, without any delay, without any waiting. It’s common to use this in the form of a command. You tell someone to do something immediately.

If you have kids—say, teenagers or younger—you probably use the equivalent of “at once” fairly frequently. Imagine you have younger kids; you’re trying to get them ready for bed. You’ve already asked them nicely a few times to brush their teeth, but they’re still playing with their toys or watching TV. At this point, you might say, “Go brush your teeth at once!”

This makes it clear that you want them to do it right now, without any more dilly-dallying, without any more delays, no more excuses, not “just five more minutes,” at once. Right now. No delays, no excuses. Go brush your teeth at once.

When talking to adults, “at once” implies some urgency. Someone in a position of authority is taking charge of the situation and telling others what to do. Think of a chemistry lab. A student in the lab spills a harmful chemical. The lab supervisor might say, “Everyone needs to get out of here at once.” That means, “everyone needs to get out of the lab right now.”

Or, imagine a hospital. A nurse finds that a patient needs a doctor’s attention immediately. The nurse might say to an assistant, “Call the doctor at once.” That means, do it right now. It’s urgent. Call her at once.

So, when you use “at once” like this, you’re asking for immediate action. But you can sometimes use it to describe immediate action. Have you ever witnessed a car crash? It’s scary. I saw one at a busy intersection in Chicago and I called the police at once. I pulled right over and called 911. And the police came and interviewed me. They asked me what I did when I saw the accident. I said, “I pulled over at once and called 911.”

Do multiple things at the same time

Now let’s take a look at the second meaning, to do multiple things at the same time. Are you good at multi-tasking? That word has fallen out of favor lately because psychologists have discovered that humans are really bad at doing multiple things at once.

Sure, we can try. But if we try to do too many things at once, then we won’t do any of them well. If you work for a big company, you probably have to attend webinars or big group conference calls. And you’re probably tempted to also do something else at the same time.

You might decide to listen to the webinar and reply to emails at once. That means, you’re doing them at the same time. But you know what? We humans are not good at this. Your attention will be on one, on the other, or on neither. But you can’t really focus on two things at once.

If you reply to an email, but you accidentally send a message to the wrong person, you might have to apologize. You can say, “I’m sorry, I was trying to do two things at once and I sent this message to the wrong person.”

All at once

A common variation on “at once” is the expression, “all at once.” When you use “all at once,” everything happens together.

We were just talking about doing multiple things at the same time. “All at once” is very common here. You might say that a parent was preparing dinner, supervising homework, and keeping an eye on work emails all at once. All these things were happening at the same time.

Another way to use “all at once” is to talk about doing things in a batch. How do you review your email? Do you interrupt your work and read all your emails one by one as they come in? Or do you wait for a few hours and review them all at once?

If you review your emails all at once, you wait until a bunch of messages have accumulated and then you read them in a group, in a batch.

A supervisor or manager might say this at work. If employees gradually finish reports, the supervisor might review the reports immediately—right after, or right as, the employees finish. Or, the supervisor might want to review them all at once. That means, she’ll wait until the work is done. Then, when all the reports are drafted, she’ll review them all at once. She’ll review them together in a batch.

Finally, you can say “all at once” when multiple things happen to you, maybe not in the same moment but in the same general period of time. You might get a new job, move to a new house, and start a new relationship all in the same month. If that happens, you can say, “So much was happening all at once; it was overwhelming.” That means, so much was happening together at the same time.

There you go. Now you’re prepared to use “at once” in your English conversations.

Remember, the first definition of “at once” means to do something immediately. It’s often used as a command, like if you tell your kids, “Go brush your teeth at once.” But it can also be used to describe immediate action like, “When I saw the car accident, I called the police at once.”

And then you learned “at once” can be about doing multiple things at the same time. If you try to do too much at once, you’ll get distracted. And then we talked about “all at once,” which is similar to the second definition. It’s about things happening together.