There are three ways “can” and “be able to” differ.
- They mean slightly different things.
- One is used more in formal English.
- One is more flexible grammatically.
This post will go over each of these differences so you know which ones to use when speaking English.
Differences in Meaning
1. “Be Able To” Is More Specific
The most fundamental difference between “be able to” and “can” is that “be able to” is more specific. “Can” serves many different functions.
- Ability: “I can speak English.”
- Possibility: “It can get hot in this room.”
- Permission: “You can leave now.”
- Request: “Can you come here please?”
For example, the question “Can you come to my party tomorrow?” could mean both “Are you able to come?” and “Is it possible for you to come?”
On the other hand, “be able to” only has one function. It describes whether or not someone has the ability to do something.
2. “Be Able To” Can Only Be Used With Subjects That Have Abilities
Sometimes, learners will write sentences like “Tickets are able to be purchased online” or “This product is able to be used in a microwave.” However, “can” is better in these cases.
- Tickets can be purchased online.
- This product can be used in a microwave.
If you say, “tickets are able to be purchased online,” it sounds like the tickets have an ability. So when you use “be able to,” try to replace it with “have the ability” and see if the sentence still makes sense.
As practice, try to think about why the following sentences use “can” and not “be able to”:
- Heart disease can be caused by many factors.
- Birds can be found on almost every continent.
(Hint: Does heart disease “have the ability” to cause itself? Do birds “have the ability” to “be found”?)
Differences in Formality
1. “Can” Is More Common in Everyday Conversation
Both “be able to” and “can” are used in informal conversation, and they are interchangeable most of the time. For example, if a friend invited you to a party, they wouldn’t notice if you said one of these sentences instead of the other:
- I don’t know if I can come to your party.
- I don’t know if I’ll be able to come to your party.
The “can’s” in the sentences below are also interchangeable with “be able to.”
- My son started swimming classes last month and he can swim now!
- Did you know that cockroaches can live almost anywhere?
English-speakers will usually just use “can,” since it’s usually clear from context that the subject has the ability to do something. So unless you’re trying to emphasize ability, you probably don’t need to use “be able to.”
2. “Be Able To” is More Common in Formal English
In formal English, and especially in writing, it’s usually better to be specific. This is why you’ll see “be able to” more often than “can” in news articles that mention ability.
You’ve probably also seen “be able to” appear in error messages when you’re using a computer. For example, if you’re buying something online and encounter some issue, you’ll see messages like:
- We are unable to process your request at this time. Please try again later.
- We are having difficulty processing your payment, so we are unable to proceed with your order.
In addition to being more specific, “be able to” also sounds more indirect and impersonal than “can.” For example, you’ve probably also received emails that say something like:
- Please do not reply to this email, as we are unable to respond from this address.
In situations like these, “unable to” sounds more polite than “cannot.” This is another reason “able to” is often preferred in formal messages.
Finally, the biggest difference between “can” and “be able to” – regardless of whether you are writing formally or informally – is that there are more limitations to how “can” can be used, so English speakers will often choose to use “be able to” instead.
1. “Can” and “Be Able To” Can Be Different in the Past Tense
Both “could” and “was able to” are used to talk about abilities people had in the past. For example, the two sentences below mean the same thing.
- When your grandma was young, she could eat five hamburgers in one meal.
- When your grandma was young, she was able to eat five hamburgers in one meal.
In the negative, they’re also the same.
- I couldn’t sleep last night.
- I wasn’t able to sleep last night.
But when we want to talk about past abilities that involve a specific incident in the past, things get tricky. For example, try to put the following sentence in past tense.
- Sally can find a job in New York after graduating.
Many learners will go for “Sally could find a job … ,” but this does not actually mean she had the ability to find a job. Here, “could” is not the past tense of “can” but its conditional form (“Sally could find a job if she tried”). The correct answers are:
- Sally could have found a job in New York after graduating.
- Sally was able to find a job in New York after graduating.
The first sentence means that she had the ability to get a job in New York, but she didn’t for some reason (e.g. maybe she wanted to work in Chicago instead). The second sentence means that she had the ability and successfully got a job in New York.
So when you’re talking about past abilities, be careful which one you choose!
2. Use “Be Able To” For Future Abilities
If you want to talk about abilities that may develop in the future, use “be able to.”
- My daughter will be able to walk in a few months.
- If I take lessons on Engoo, I will be able to speak English confidently.
If you just want to talk about future plans, you can use both “can” and “be able to.”
- I can come to your party tomorrow.
- I’ll be able to come to your party tomorrow.
3. Use “Be Able To” After Other Verbs
Since “can” is a modal verb, it can’t be used after other verbs. This is why the following sentences use “be able to.”
- Applicants must be able to speak fluent French.
- I want to be a nurse, because I want to be able to help people who are sick.
4. “Be Able To” Can Be Used With Other Tenses Too
- I wonder what it’s like not being able to swim.
- She’s recovered her appetite and has been able to eat a lot more lately.
That was a lot of information, so here’s a quick summary to help you review.
- “Can” is used most of the time in casual conversation.
- “Be able to” is more specific to ability.
- “Be able to” is more flexible. It can be used with any verb and tense!
- “Was able to” is used for successful one-time events in the past and “Could have + past participle” for unsuccessful ones.
Now it’s time to practice! The following sentences all have a mistake. Try to find them.
- Your email is unable to be delivered.
- You don't need to can read music to learn guitar.
- I have not can log into Facebook since last night.
- The Great Wall of China is unable to be seen from the moon.
- Applicants must can speak fluent French.
To find out the answers, sign up for a free lesson! We have thousands of tutors available 24/7 and also plenty of free grammar materials you can study with. You’ll also be able to practice grammar while having real conversations and getting useful feedback.