So, as I said, there's a theory of intelligence called the Cattell-Horn-Carroll theory of Intelligence. This is the best known compromise between the singular intelligence theory and the multiple intelligences theory. This theory focuses on the idea that intelligence comes in two distinct forms. Fluid and crystallized intelligence. Now if you remember from lesson five on development, fluid intelligence was the raw intelligence. This is the processing power and it's relatively free from the culture and environmental influences. Crystallized intelligence on the other hand reflects what you learn from your environment and your experiences. Let's look at the Cattell-Horn-Carroll theory as a hierarchy. It focuses on three broad levels. The first level is the general intelligence or the g factor. The second level is the broad level of intelligence. They're usually your general abilities. This is where your crystallized intelligence and your fluid intelligence comes into play. As well as things like, your general memory, or your processing speed. Now there's other abilities that go in this level, but these are the main four. And finally the last level, is the narrow level. This consists of specific forms of cognitive abilities from each of the broader domains. For example, with crystallized intelligence, it would be things like reading, spelling, or language comprehension. And for fluid intelligence, it would be things like speed of reasoning or facial reasoning. The main idea here is that intelligence would be a hierarchy. We start with the general idea of intelligence, the g factor, one intelligence. Then we go to a more broad level. This includes abilities such as crystallized and fluid intelligence, or memory and processing speed, among others. Then finally, from there, it narrows down into specific abilities for each one of these.