The Ultimate Guide to Explaining "Can" and "Be Able To"
"What's the difference between 'can' and 'be able to'?"
"Should I use 'can' here or 'be able to'?"
"What about 'I am unable to can'?"
With the exception of the last question (which is, of course, a joke), you've probably been asked something along these lines many times during your career as an online tutor.
So in order to put all our students' questions, concerns, fears, and nightmares about this aspect of grammar to rest, we've compiled this ultimate guide to explaining "can" and "be able to."
This guide is made of the following three parts:
We also have a summary at the end for those of you who want a one-minute version of this post!
1. Grammar
The biggest difference between “can” and “be able to” is the grammar. If sentences were puzzles, "be able to" would be the kind of puzzle piece that could be slotted into many places, while "can" only fits in one.
In other words, a lot of times, "be able to" and "can" are interchangeable meaning-wise, but people use "be able to" because using "can" wouldn't make sense grammatically!
🔮 Future Abilities? Use “Be Able To”
When you want to talk about an ability someone might develop in the future, "be able to" is the grammatical choice.
- My daughter will be able to walk in a few months.
- After taking my classes, you will be able to speak English fluently.
Using "can" when you are talking about a future ability would be confusing. For example, if someone said "My daughter can walk in a few months," the listener might need some clarification: "So, can your daughter walk now? Or will she be able to walk in a few months?"
(You might be wondering why both "I can come to your party" and "I'll be able to come to your party" are acceptable. That's because these sentences are referring to future plans – not abilities.)
⌛ Specific Events in the Past? Use “Be Able To”
Both “could” and “was able to” are used to talk about abilities people had in the past. For example, the sentences below mean the same thing regardless of which option is used.
- When your grandma was young, she could/was able to eat five hamburgers in one meal.
- I couldn’t/wasn't able to sleep last night.
When talking about specific events in the past, could is sometimes ambiguous. For example if we wanted to express that Sally had the ability to find a job and she did just that, we might say "Sally could find a job."
But in this sentence, "could" might also be the conditional form of "can." So the sentence could be understood as "Sally had the potential to find a job (but maybe she didn't)." This is another time when "be able to" makes more sense than "can."
- Sally was able to find a job in New York after graduating.
🏃 After Other Verbs? Use “Be Able To”
Another time when only "be able to" is acceptable is after other verbs. Since “can” is a modal verb, it can’t be used after other verbs.
- 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.
"Applicants must can speak fluent French" and "I want to can help people" simply sound weird.
🪄 In Other Grammatical Forms? Use “Be Able To”
As a modal verb, “can” also does not have a continuous (-ing) form or a perfect form. So when a learner wants to talk about ability using another grammatical form (i.e. tense or aspect), they'll need to use “be able to.”
- 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.
2. Meaning
In addition to the grammar, meaning is another important way that "can" and "be able to" differ.
💪 Subjects Don’t Have Abilities? Use “Can”
Sometimes, learners will write sentences like “Tickets are able to be purchased online” or “This product is able to be used in a microwave.” These sentences probably sound weird to you. After all, tickets and products don't really have abilities! That's why “can” sounds more natural in these cases.
- Tickets can be purchased online.
- This product can be used in a microwave.
A trick you can teach students is that when deciding between "be able to" and "can" (and after considering the grammatical aspects), they can try phrasing the sentence with "have the ability." If the sentence makes sense, then they can use "be able to." If not, they should stick with "can."
For example, the following sentences wouldn't make sense with "be able to," because heart disease doesn't “have the ability” to cause itself and birds don't "have the ability" to be found.
- Heart disease can be caused by many factors.
- Birds can be found on almost every continent.
3. Formality
Finally, the last way in which "be able to" and "can" differ is in formality. While they're both used in everyday conversations for the reasons we've discussed above (grammar and meaning), "be able to" is more common in formal English.
After all, formal English – especially writing – calls for specificity. This is why you’ll see “be able to” more often than “can” in news articles that mention ability.
In addition, “be able to” sounds more indirect and impersonal than “can.” This is why automated messages from computer programs often use "able to" instead of "can."
- We are unable to process your request at this time. Please try again later.
- Please do not reply to this email, as we are unable to respond from this address.
However, we wouldn't recommend dwelling on formality too much. For one, standards for formality change. For example, automated messages seem to be using "can" more and more these days (e.g. "Cannot connect to this network, "Cannot connect to the app store," etc).
Further, overemphasizing formality may lead students to think that they should only use "can" in informal contexts and "be able to" in formal ones when grammar and meaning should play a much bigger role in this decision.
📌 Takeaways
That was a lot of information, so here’s a quick summary:
- Grammar
- “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.
- Meaning
- Use "can" for subjects that don't have abilities.
- Phrase sentences using "have the ability" to see if they would make sense with "be able to."
- Formality
- Compared to grammar and meaning, formality plays a smaller role in deciding whether to use "be able to" or "can."
- "Be able to" is more common in formal contexts.
We hope this guide helps you the next time you need to explain this to a student. Happy tutoring!
