They are a almost the same but to start with they can be homonyms for other things too. For example. Smart can be pretty. Bright can be clear. Then clever can be a little negative, intelligent is neutral. For example, if you say, 'that is a clever trick', you can indicate that the trap you fell into was cleverly thought out, well thought, but that does not mean that you think that the person that has invented that trick is also very intelligent.

Hi Nico, you can always use "smart". "Intelligent" is more formal and implies someone has been well educated. "Clever" means ability to figure things out for oneself. "Bright" is casual language and usually used to refer to a child or young adult as being gifted in some regard.

A couple of things to add to the other members' excellent explanations: 'smart' is used less in the UK than it is in the USA. The main meaning of 'smart' in British English refers to dress and appearance, in contrast to casual. (eg 'You need to dress smartly for your job interview - make sure you put on a smart suit). 'smart' is sometimes used in Britain the American sense of 'clever', particularly in set phrases such as 'That was a smart move!' 'He's a pretty smart businessman' or 'Don't give me any of your smart answers!' . In this last example, it has a negative implication ie rude and cheeky. As the other members have said, a clever person is good at working things out for themselves, often to their own advantage. Intelligent is somehow deeper, a reference to your brain power rather than your behaviour. And, again as others have said, 'bright' is a term that adults use for children and young people. So it wouldn't be appropriate to use this for one of your colleagues, for example - it would sound condescending.