Grammar-QuizzesVerb PhrasesVerb GroupsModals › Can vs. Could

Can vs. Could

Physical, mental, past and potential ability

super computer contestant
 

 

 

General/Physical vs. Mental Ability

PHYSICAL ABILITY

general abilityCan expresses opinion about general or physical ability.  Something or someone is able to do something.  (strong or powerful enough, capable of)

CAN / COULD PLAIN FORM VERB

"Watson", a super computer, can

answer questions in "natural language".

Watson can

access 200 million pages of information in seconds.

Watson cannot

think like a human. It can only learn.

In most cases, the computer could

win(come up with correct answers first)

MENTAL ABILITY

mental abilityCan also expresses opinion about mental ability.  Something or someone knows how to do something.

CAN / COULD PLAIN FORM VERB

Ken Jennings can

speak on a wide variety of subjects.

Ken can

play a game to win.

Ken could

outsmart his opponents every time.

Often, Ken could

outsmart Watson's reasoning ability.

 

Watson is an artificial intelligence computer system capable of answering questions posed in natural language, developed by IBM. http://en.wikipedia.org/wiki/Watson_(computer)

Jeopardy – a game show in which contestants are give the answer and must come up with the question

Also see   May / Can  (permission)   

 

 

 

 

 

 

Be Able / Can / Could

Past success and future potential

 

 

 

A single past event – was/were able to

REACHED A GOAL

managed to reach a goalWas / were able to express opinion about reaching a  particular goal or success.  Something or someone managed to do something. (single event–past)

WAS / WERE ABLE INFINITIVAL VERB FORM

IBM engineers were able
(managed)

to design a computer that uses "natural language".

After several tries, IBM engineers were able

to program Watson to win a match.

Ken Jennings was able to

win 75 Jeopardy matches.

Watson was not able

to understand his opponent's answers.

POTENTIAL

potential abilityCan expresses opinion about potential ability.  Something or someone has the potential or is likely to do something. Both can and could express future potential.

CAN / COULD PLAIN FORM VERB

In the future, Watson can

help suggest treatment options to doctors.

Watson can

analyze a patient's symptoms and medical history.

Ken Jennings can

use his celebrity to endorse products.

One day, IBM could

build a computer with cognitive power.

 

cognitive (Adj) – having mental processes of perception, memory, judgment, and reasoning,

contestant (N) – person playing or competing in a game or competition

opponent (N) – the person you play against in a game.

 

 

 

 

 

 

Could / Was Able

Express past ability in general or in particular

 

 

Could vs. Was/Were able

COULD – GENERAL ABILITY

mental abilitygeneral abilityCould is used for ability with a general sense of time. Could is not used for a moment of completion or success, a particular and singular time pinned to the past . It expresses a "timeless" ability.

MULTIPLE PAST EVENTS OR ONGOING

I practiced a lot during the winter.

By summer, I could drive pretty well. (general timing)

If I wanted to, I could drive to work or to the store.

Before 1935, anyone could drive. Now the state requires a license.

Only state residents could apply for a driver's license.

 

WAS ABLE  – PAST ABILITY

managed to reach a goalWas/Were able expresses ability with a particular and singular time pinned to the past, a moment of completion or success.  A similar meaning is expressed by  "managed " + infinitive or "succeeded in" + gerund.

SINGLE PAST EVENT – MOMENT OF COMPLETION

I practiced a lot during the winter.

By summer, I was able to pass my driving exam.

By summer, I could  pass my driving exam. (single event)

I was able to get my driver's license. 

I managed to get my driver's license.  

I succeeded in getting my driver's license.

 

Eng-US: license (n./ v.) , Eng–Br: licence (N); Eng-US: practice (n./ v.); Eng–Br: practise (V)

pop question Pop-Q Resultive "so".

 

 

 

 

 

 

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.
 

 

 

 

 

 

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Grammar Notes (Advanced)

Traditional and Linguistic Description

 

 

 

Traditional / ESL and Linguistic Descriptions

TRADITIONAL & ESL DESCRIPTION LINGUISTIC DESCRIPTION
AZAR HUDDLESTON

can / could (Azar 10.1-4)

  • possibility
    • modal → He could be sick.   (possibility – 50% degree of certainty);
    • past modal modal → He could have been sick.   (possibility – < 50% degree of certainty)
    • negative modal → He couldn't be sick.   (possibility – 99% degree of certainty)
  • past modal Tom could lift the box. Tom said he could speak French.  (ability)
  • polite request Could you help me?
  • suggestion (an option; one of several ideas) →  You could ask a different doctor. (20-4)

 

can / could  "Mood and Modality" (Huddleston 3 §9)

  • possibility (epistemic) → weak commitment → He can't have done it.(neg. only) / He could be the killer. [possibility]
  • possibility (deontic ) → He can have one more cookie. [permission]
  • possibility (dynamic) (3 §9.3.3)
    • You can always say "no". [reasonable/ acceptable]
    • Rain can get in. [circumstantial possibility]
    • Dogs can bite. [existenitial]
    • He could set a record today. [potential ability]
    • He can / could speak Swahili. [actualized ability]
  • backshift → He said he could speak Swahili. [actualized ability] He thought that Valjean could be the killer. [possibility]
  • polite form–distancing ("modally remote preterite") → Could you help me?  (3 §9.8.3)
     
SWAN BIBER

can/ could  (Swan 122-5)

  • ability
    • presentI can read Italian. (knowledge, skill, strength)  
    • past →  I could read quickly.  He said he could read Italian. After studying a year, I was able to read Italian. (122.5)
  • common or typical → It can be hot here in summer.
  • possible in the situationWe can go to Athens.
  • soft suggestionWe could try a different approach.
  • unrealized pastWe could have gone to Athens, but we didn't
  • chances (possibility) → It could rain this afternoon. (122.8)
  • permissionCould we have some cake?  (more polite than can) (124)
  • requests, orders, and suggestionsCould we have some cake?  (124.6)
  • criticismYou could have told me you were dating my girl.
  • indirect speechI asked if they could give me some help. 

 

can / could (Biber 6.6.4.1)

permission / possibility / ability: can, could

Could and might are much more common expressing logical possibility than permission or ability.

In contrast to the typical functions of can, the modal could usually marks logical possibility in conversation, expressing a greater degree of uncertainty or tentativeness.  That could be her.  It could be anything you choose.

Epistemic Stance.modal Verb in extrinsic sense Without… collaboration there could be interference… (973)

 

 

Resources

  • Azar, Betty Schrampfer, and Stacy A. Hagen. Understanding and Using English Grammar. 4th ed., Pearson Education, 2009.
  • Biber, Douglas, and Stig Johansson, et al. Longman Grammar Of Spoken And Written English. Pearson Education, 1999.
  • Huddleston, Rodney D., and Geoffrey K. Pullum. The Cambridge Grammar of the English Language. Cambridge UP, 2002.
  • Swan, Michael. Practical English Usage. 3rd ed., Oxford UP, 2005.

 

 

 

 

Practice1

Various Abilities

managed to reach a goalpotentialphysical abilitymental ability

 

 

What is the meaning ?

  1. Select the response from the list that best completes the sentence. 
  2. Compare your response to the feedback by clicking the "Check" or the "Check 1-15" button.

 

1.

2.

3.

4.

5.

 

 

 

 

 

 

 

Practice 2

Driving Skills

driver
 

 

Which phrase can replace the modal in each of these sentences? 

  1. Select the response from the list that best completes the sentence. 
  2. Compare your response to the feedback by clicking the "Check" or the "Check 6-10" button.

 

6.
When I was little , I wanted to drive, but I couldn't.




7.
Now, I am taking a driving course so that I can drive a car.



8.
If a driver is not careful, he or she can cause an accident. 



9.
After practicing for a month, I was able to shift gears without difficulty.




shift gears – manually change the speed of the car; first / second / third / fourth gear

10.
From then on, I could change gears with ease.