[Grammar] can vs may

[constantinusphilo]

Some grammar books state that 'can' expresses 'theoretical' possibility, while 'may' expresses 'factual' possibility. The others, like A Comprehensive Grammar of the English Language by Randolf Quirk, state that 'may' expresses 'epistemic' possibility. Therefore, according to them, there is a difference in meaning between 'The railroads can be improved' and 'The railroads may be improved.' The first one means: 'It is possible for the railroads to be improved'. The second one means: 'It is possible that the railroads will be improved.'
However, I am not sure I get the difference between the two, unless the first means something like 'in theory', and the second 'there are concrete plans to carry out their improvement'.

 

[5jj]

Therefore, according to them, there is a difference in meaning between 'The railroads can be improved' and 'The railroads may be improved.' The first one means: 'It is possible for the railroads to be improved'. The second one means: 'It is possible that the railroads will be improved.'.

I can't find those examples. What page are they on?

 

[Glizdka]

I like to think of can as an expression of possibility, and may as an expression of probability.

 

[constantinusphilo]

The examples are mine.