Diferencias Y Semejanzas Cualitativa Y Cuantitativa

Ability in present and past
*Use can or be able to to talk about ability in the present.
 Examples: She can do computer graphics
She's able to do computer graphics
*Use either could or was/wereable to to talk about ability(but not a specific achievement) in the past.
 Examples:Sam could read when he was four.
 He was able to use acomputer too.
--Be Careful:Use managed to or was/wereable to to talk about a specific achievement or a single event in the past.
 Examples:She managed to delete the virus from her computer.
 He was able to fix his computer when it broke down.
 *Useeither could or was/were able to in negative sentences about past ability.
 Examples:I couldn't do spreadsheets
 I wasn't able to do one problem.
--For forms and tenses other than the present orpast, use be able to.
 Examples:Jen wants to be able to write software. (infinitive)
By June she will be able to complete her computer class. (future)
Past ability & possibility
 
In thepresent tense we use ‘can’ to talk about a general ability – e.g. I can swim – and also for ability at a particular moment – e.g. I can see you! The rules for talking about past abilities are different.General ability

We use could to talk about general abilities in the past.
* He could speak fluent French when he was 5.
* I could read before I started school.
Ability on one occasionHowever, when we talk about ability on one particular occasion, we can’t use could
* The burglar was able to get in through the bathroom window.
* The burglar managed to get in through thebathroom window.
We have to use was able to or managed to. We can’t use could.
* The burglar could get in through the bathroom window.
Ability on one occasion - negative

When we talk about aparticular occasion when something wasn’t possible, we can use wasn’t/weren’t able to, didn’t manage to, or couldn’t
* The burglar wasn’t able to get in through the window.
* The burglar didn’t...