4.121 capability: 'can' and 'could'

'Can' and 'could' are also used to say that something or someone is capable of having a particular effect, or of behaving in a particular way.

• It can be very unpleasant.
• Art can be used to communicate.
• I think unions can be stupid, intransigent, pigheaded.
• He could be very stiff, could Haggerty.
• He could really frighten me, and yet at the same time he could be the most gentle and courteous of men.