These verbs usually mean the same with or without can.
- I (can) remember London during the war.
She can speak Greek / She speaks Greek.
I can’t/don’t understand.
Can/Do you play the piano?
We do not use these verbs in progressive tenses when they refer to perception (receiving information through the eyes, ears etc). To talk about seeing, hearing etc at a particular moment, we often use can see, can hear etc.
- I can see Susan coming, (not I’m seeing . . . )
I can hear somebody coming up the stairs.
What did you put in the stew? I can taste something funny.