Theories of intelligence
There are a whole host of theories about intelligence, none of which really agree with each other. Every approach to thinking or the mind comes up with it's own different theory of what intelligence is, each from it's own different perspective, with it's own assumptions, and often contradicting at least one other theory.
The behaviourists seem to believe that there is no such thing as high level intelligence. The entire mind is built from the ground up from simple "Stimulus-Response" pairings, building higher and higher level functioning out of this simple technology. The surprising thing is that it seems to work as a model for some types of tasks. In fact it is this basic idea that is the basis for neural networks in artificial intelligence. Unfortunately, the further away you get from the initial input, the harder it is to get the neural nets to produce sensible answers. They are even managing to translate the structures of neural networks into higher level symbolic logic using the technology of fuzzy logic.
The people who are into General semantics have a different model of the nature of intelligence. Their founder Count Alfred Korzybsky believed that intelligence was an emergent property of life, which was an emergent property of complex chemistry. There is even some evidence to suport his belief with the discovery of auto-catalytic sets of chemicals, which confirms the first step in his theory. If you wish to learn more about his views, his book "science and sanity" sets out a wonderfully detailed step by step path to some quite remarkable conclusions. They are also doing detailed work at the institute of general semantics to try and find better ways of using the faculties that are inherent in the potential of the mind.
Then there was the belief in an overall general intelligence, where your intelligence was composed of a single component that was easily measured on intelligence tests. While they proved to be partially right (about 70% of your IQ is this factor usually refered to as "g"), the improvement of the testing methods, combined with the direct measurement of "g" by a technique called Evoked Potential proved that they could not be totally right.
Gardener's multiple intelligences
This lead Howard Gardener, by 1980 to extend the theory of general intelligence to include a set of Specific Intelligences which make up the other 30% of your IQ score. There has been some sucess in finding evidense to support some of gardener's seven catagories, and the general technique of spotting extra components that go to make up your IQ is extendable to a lot more than 7 catagories.
This leaves us with multiple incompatable theories, all based on some evidence form some method of thinking about thinking, which gradually as more evidence comes in will have to be used to genarate yet another set of new theories which will integrate various of the sets of evidence. The theories show here are only special in that it was possible to find the information for them relatively easily, and there are plent more theories out there which could also go into this, but they probably wouldn't extend the coverage very much.
Basically, the science of scientifically investigating the brain, intelligence, and how they work is just too new. As more evidence comes in, theories will be change, merge, be thrown out completely, and generally mutate. They have since 1908, and there is no reason to believe that the greater amounts of evidence coming in every year will slow this trend down.