Someone steals a pen and is asked: 'Did you steal the pen?'
They reply: 'No'
It is said to them: 'You are a liar.' Does this nominative sentence not suggest that they are a liar as a habit or that lying is more of a permanent characteristic of their personality more than a verbal sentence such as: 'You have lied.'
Thus, based on that, would it be wrong to describe a person using a nominative sentence when a person does not possess a certain attribute as a permanent feature?
So if somebody did something foolish, which was not their habit, and it was said to them: 'You are a fool.' it would not be as reflective of the situation as using a verbal sentence such as: 'You have been foolish.' or are the two interchangeable?