Can / Could
Expressing ability
Can expresses four types of ability:
| PHYSICAL ABILITY | MANAGE TO, SUCCEED IN | MENTAL ABILITY | POTENTIAL ABILITY |
|---|---|---|---|
 |
 |
 |
 |
The Internet can transfer video files onto personal computers. |
I was able to buy an iphone after saving for two months. (a single past occurrence) |
Most people can use computers to submit their tax information. |
Contestants can become famous after appearing on American Idol. |
Also see May / Can (permission)
Physical Ability
| CAN / COULD | BE ABLE TO |
|---|---|
Use can or could (past tense) to indicate physical ability. |
Also, use (be) able to to indicate physical ability. Note that the past tense forms, could vs. was able to may differ in meaning. |
High-speed connections can download large music files quickly. |
High-speed connections are able to download large video files in seconds. |
Dial-up (telephone) connections could download music files slowly. |
Dial-up (telephone) connections were able to download music files slowly. |
Smart phones can connect to the Internet. |
Smart phones are able to connect to the Internet. |
Older telephones could only call other telephones. |
Older telephones were only able to call other telephones. |
Manage to, Succeed in
| COULD – multiple events or ongoing activity | WAS ABLE TO – single event |
|---|---|
Could is used for multiple occurrences of ability or ongoing ability. Could is not used for a moment of completion or success, a one-time event. (Could does not restrict or limiit the event to a single moment.) |
Use be able to for a single occurrence, a moment of completion or success; "He managed to pass his exams." (followed by an infinitive) "He succeeded in passing his exams." (followed by a gerund) |
I practiced a lot during the winter. By summer, I could drive pretty well. (habitual activity) |
I practiced a lot during the winter. By summer, I was able to pass my driving exam. (single event) |
Through hard work and research, they have made progress. (continual activity) |
Through hard work and excellent research, they were able to find a cure for the disease. |
After saving for five years, they were realizing their dreams. (continuous activity) |
After saving for five years, they were able to buy their own home. (single event) |
Eng-US: license (n./ v.) , Eng–Br: licence (n.)
Eng-US: practice (n./ v.) , Eng–Br: practise (v.)
Mental Ability
| CAN / COULD | KNOW HOW TO / KNEW HOW TO |
|---|---|
Use can or could (past tense) to indicate mental ability. |
Also, use know how to or knew how to (past tense) to indicate mental ability. |
We can solve our economic problems. |
We know how to solve our economic problems. |
Previously, we could solve our economic problems |
Previously, we knew how to solve our economic problems. |
Engineers can design safer buildings. |
Engineers know how to design safer buildings. |
Before the earthquake, engineers could design safe buildings, but they didn't. |
Before the earthquake, engineers knew how to design safe buildings, but they didn't. |
Potential / Probable Effect
| CAN / COULD | HAVE POTENTIAL |
|---|---|
Use can or could for the possibility that something will develop in a particular way, or have a particular effect. (Could is used in past and present tense sentences.) |
Use has / have the potential to for the possibility that something will develop in a particular way, or have a particular effect. |
Overspending can crash the economy of a country. (present tense) |
Overspending has the potential to crash the economy of a country. |
Overspending could crash the economy of a country. (present tense) |
Overspending had the potential to crash the economy of a country. (past tense) |
Currently, people can become famous by appearing on YouTube. (present tense) |
Currently, people have the potential to become famous by appearing on YouTube. (present tense) |
In the past, people could become famous by appearing on television. (past tense) |
In the past, people had the potential to become famous by appearing on television. (past tense) |
Sentence Types
Word Order
| MODAL | SUBJECT | MODAL / VERB EXPRESSION | MAIN VERB | OBJECT PHRASE |
|---|---|---|---|---|
STATEMENT
|
Jack |
can |
cook |
dinner. |
Jack |
is able to |
fix |
your bicycle. |
|
Jack |
knows how to |
use |
a computer. |
|
QUESTION What can |
Jack |
|
do? |
|
Can |
Jack |
|
lift |
that computer by himself? |
Is |
Jack |
able to |
drive |
your car? |
Does |
Jack |
know how to |
use |
a computer? |
NEGATIVE |
Jack |
can't |
come |
home early. |
Jack |
is not able to |
come |
home early. |
|
Jack |
doesn't know how to |
come |
home early. |
|
PAST |
Jack |
could |
stay up |
all night when I was 18. |
Jack |
was able to |
stay up |
all night on New Years. |
|
|
Jack |
knew how to |
use |
a computer |
WTH AN ADVERB |
Jack |
can usually / usually can |
cook |
dinner in an hour. |
Jack |
is sometimes able to |
do |
his homework. |
|
|
Jack |
always knows how to |
fix |
a computer problem. |
W/ NEG. ADVERB *Seldom can |
Jack |
|
get |
his homework done. |
*See Adverbs of Frequency for sentence examples.
Practice1
What is the meaning ?
- Select the response from the menu that best describes the meaning of can in the sentence.
- Click the check button to compare your response to the answer.
Practice 2
Means About the Same
Which phrase can replace the modal in each of these sentences?
*indicates an incorrect answer.