[Grammar] Can or could

[Jlsg]

Do I use can or could in this situation?

They were so hungry that they could/can eat a horse if they wanted.

Are there any situation when you use can instead?

 

[Barb_D]

I'm so hungry I could eat a horse.
I was so hungry I could have eaten a horse.

 

[Jlsg]

I'm so hungry I could eat a horse.
I was so hungry I could have eaten a horse.

Thank you for your reply. But I don't really understand. Do we use could in your first sentence because it is a possibility even though you start off with present tense?

If I change to this sentence

His leg was so strong that he can run in marathon if he wanted to.

Is this correct? Or should I have use could instead?

 

[Tdol]

They were so hungry that they could/can eat a horse if they wanted.

Are there any situation when you use can instead?

Not with this sentence.

 

[GoesStation]

His leg was so strong that he can run in marathon if he wanted to.

Is this correct? Or should I have use could instead?

You have to use could. You can only use can if you're talking about a factual situation in the present tense: He's in such good shape that he can run ten miles without getting tired.

 

[jutfrank]

His leg was so strong that he can run in marathon if he wanted to.

Is this correct?

No, it's not correct.

Look:

They are so hungry that they could eat a horse. [present]

The were so hungry that they could have eaten a horse. [past]

It is easy to get confused with can and could.

Sometimes, can means present ability and sometimes could means past ability.
Sometimes, could means present or future possibility and could have + verb3 means past possibility.

 

[Tdol]

His leg was so strong that he can run in marathon if he wanted to.

Is this correct? Or should I have use could instead?

You should use could because it is still an imaginary situation. You could use can in a sentence like this, where it descries a real situation:

His legs are so strong that he can run a marathon every week without any problem. (He does run a marathon a week.)