We use can + infinitive or am /are /is allowed to + infinitive to say some thing is permitted in the present
at home I can only watch TV when my homework is finished
my brother is allowed to play football every weekend


we use cant +infinitive or am /are/is not allowed to+ infinitive to say something is not permitted in the present
her record company says she cant stop touring
you aren't allowed to drive and use a normal mobile phone at the same time

we use could +infinitive or was /were allowed to + infinitive to say something was permitted in the past
my grandparents could eat chocolate just once a week when they were children
her parents were vary proud of her.so she was allowed to appear on TV



we use couldn't+ infinitive or wasn't/weren't allowed to +infinitive to say something wasn't permitted in the past
my mum couldn't wear trousers at school because it was against the rules then
when I was younger, I wasn't allowed to go to the mall