Most adults fail to learn a foreign language no matter how many years they sit in a classroom or live where the language is spoken because they spend nearly all of their study time learning “about” their target language instead of the language itself. This is the critical difference between “studying” and “learning”.
The term “Multiple Intelligences” was first coined by Harvard psychologist Howard Gardner. His theory is spelled out in the 1983 book, Frames of Mind: The Theory of Multiple Intelligences. In the book, Gardner posits that humans possess many varied types of intelligence, not just one. This stands in stark contrast to IQ and standardized testing, both of which look at intelligence as a one-dimensional concept: you either have it or you don’t. While Gardners’s work is still somewhat controversial, I think it is a helpful way to frame intelligence and useful tool for choosing effective language learning methods and materials for oneself.