As we know, modal verbs "could" & "can't" can be used to guess something or state an ability.


She could be at home now (=It is possible that she is at home now. The chance is 50%)

She can't be at home (=I am quite sure that she is not at home now. The chance is 85-90%)

I could swim (= I had an ability to swim in the past)

I can't swim (=I don't have an ability to swim now)

Now, see this conversation in "The Social Network":

Mark: Did you know there are more people with genius IQs living in China than there are people of any kind living in the United States?

Mark'girlfriend: That can't possibly be true.

Mark: It is.

Mark's girlfriend: What would account for that?

Mark: Well, first, an awful lot of people live in China, but here's my question. How do you distinguish yourself in a population of people who all got 1600 on their SATs?

Mark's girlfriend: I didn't know they take SATs in China.

Mark: They don't. I wasn't talking about China anymore, I was talking about me.

Mark's girlfriend: You got a 1600?

Mark: Yes. I could sing in an a capella group, but I can't sing.

Mark's girlfriend: Does that mean you actually got nothing wrong?

Mark: I could row crew or invent a $25 PC.

My question is:

Do "could" & "can't" in the sentence "I could sing in an a Capella group, but I can't sing." express a guess or an ability?

Does "I could sing in an a capella group" mean "I guess I have a 50% chance of singing in an a capella group now" or "I had an ability to sing in an a capella group in the past"?


Does "but I can't sing" mean "I am quite sure that I have a 90% chance of not singing in an a capella group now" or "I don't have an ability to sing in an a capella group now"?

  • I think the eighth line should be: "Mark: Yes. I could sing in an a cappella group, but I can't sing." A cappella is singing without musical accompaniment, so skill become more important than otherwise. I haven't seen the movie, but more context needs to be added around the last three lines to understand what he means. Seems like overt bragging though. Maybe he is thinking "with enough brains talent doesn't matter".
    – user3169
    May 26, 2018 at 5:38

1 Answer 1


I don't think your confusion lies with the meaning of "could", but with the use of "can't".

"Can't" or "cannot" literally mean that something is not possible. One hundred percent not possible, if meant literally. However context is king, and the words can mean something slightly different in certain contexts.

First of all, the word could be used to express surprise in the face of something that actually is happening against all odds. For example:

-Donald Trump is the new president of the USA.
-He can't be!

But also, and I believe this is the case in your quote, it can be used to mean someone is not very good at something.

I can't sing

..doesn't necessarily mean that the person cannot open their mouth and have a sound come out of it. It likely means they don't have a great singing voice, or are tone-deaf and can't hit the right note.

I think in the context of your quote the implication is that a perfect SAT score of 1600 opens lots of opportunities to people that they either don't want to take or shouldn't take. Mark is saying that he could join an a Capella group, perhaps because his SAT score qualifies him to, yet he is not qualified in the sense that he has a terrible singing voice.

Again, with this "other meaning" of can't, context is important.

For example:

I can't walk

..could mean different things depending on context. If somebody in a wheelchair said this to you then you might well assume that their legs do not work and "can't" literally means walking is impossible.

However if you suggested to an able-bodied friend that you walk a distance instead of taking transport and they said this you would assume that there was some other reason preventing them, or that their walking was limited or not good enough to go such a distance.

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