What part of speech is “cannot”

'cannot' is a modal auxiliary verb used to express incapability, impossibility, or prohibition. It's a more formal version of the contraction 'can't.'

'cannot' is used to indicate something that is not possible or is forbidden, denote an inability to do something, express a logical impossibility.

You cannot enter this area without proper identification.

He cannot see without his glasses.

Water cannot flow uphill without external forces acting on it.

'cannot' is often used in more formal contexts, while 'can't' is more common in spoken English and informal writing. 'Cannot' is written as one word. A common mistake is to separate it into two words as 'can not.' While 'can not' is technically not incorrect, it's less standard and can sometimes lead to ambiguity. For example, 'I cannot run' (I am unable to run) vs. 'I can not run' (I am able to choose not to run). 'Cannot' is often followed by an infinitive verb to indicate the action that is impossible or prohibited, e.g., 'cannot do,' 'cannot see,' 'cannot understand.' In negative questions, 'can't' is often preferred over 'cannot' for brevity and rhythm, e.g., 'Can't you see?' rather than 'Cannot you see?'