Howard Gardner concluded from his research that human intelligence is like a jigsaw puzzle of nine pieces, all of equal value and importance. According to Gardner, these are characteristics that classify what kind of intelligence each person possesses, as well as what facilities they bring to our lives.
Prior to this discovery, the main theory that dealt with intelligence was that of Alfred Binet, who created an intelligence test that measured IQ (intelligence quotient), but his area of expertise was limited only to mathematics and language.
