Intelligent and smart are the same. Smart is more informal. In an official report or
scientific article, we would probably use “intelligent,” and in everyday speaking, we
would probably use “smart.”
▶️ The stereotype that blondes are less intelligent is unsupported by scientific
evidence.
▶️ Your daughter is 3 years old and she already knows how to read? She’s so
smart!
The word clever has the connotation of being smart in a creative way. If somebody
is able to find an unusual and innovative solution to a problem, which nobody else
imagined, we would describe the person as clever. A clever person can be good or
bad:
▶️ A person who creates an interesting new method of reusing recycled material
is clever.
▶️ A thief who invents a creative way to break into a bank and rob it is also
clever.