Can / Could
Expressing ability
Can expresses four types of ability:
| PHYSICAL ABILITY | MENTAL ABILITY | POTENTIAL / POSSIBILE ABILITY | SUCEED IN |
|---|---|---|---|
 |
 |
 |
 |
The Internet can transfer video files onto personal computers. |
People can use computers. |
Contestants can become famous after appearing on American Idol |
I was able to buy an iphone after saving for two months. (a single occurrence) |
Physical Ability
| CAN / COULD | BE ABLE TO |
|---|---|
To have the physical ability. |
To have the physical ability. |
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 call another phone. |
Older telephones were only able to call call another phone. |
Mental Ability
| CAN / COULD | KNOW / KNEW HOW TO |
|---|---|
To have the mental ability or capacity |
To have the mental ability or capacity |
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 / Possibility
| CAN / COULD | HAVE / HAD POTENTIAL |
|---|---|
Use can or could for possibility of; or having the potential to. Could can be used in past or present tense. |
To have the possibility of; be capable of becoming |
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) |
Succeed In
| COULD – multiple/ongoing activity | WAS ABLE TO – single event |
|---|---|
Could is not used for "suceed in doing something", a single event of completion. It is used for multiple occurrences: habitual activity(continuous) or onging activity (continual). |
Used be able to for a single occurrence, a moment of completion or success; "manage to" |
I practiced a lot so that by summer, I could drive pretty well. (habitual activity) |
I practiced a lot so that by summer, I was able to get my driver's license. (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) |
Also see So used with Could
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 yourself? |
|
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. |
||
PAST
|
|
Jack |
could |
stay up |
all night when I was 18. |
Jack |
was able to |
stay up |
all night on New Years. |
||
WTH AN ADVERB
|
|
Jack |
can usually |
cook |
dinner in an hour. |
Jack |
is always able to |
do |
do my homework. |
||
W/ NEG. ADVERB |
*Seldom can |
Jack |
|
get |
his homework done. |
*See Adverbs of Frequency for sentence examples.
Practice
Determine the Meaning
What is the meaning of "can" in the sentences?