A few years ago, I was looking for a semi-popular book I could recommend to people on dual systems theory. I picked up Kahneman's TFS expecting it to be a good choice, but was very disappointed. His logic was sloppy and bombastic, but what I found most irritating was that he would constantly, like maybe every other page, slightly misrepresent other people's work.

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Dual systems theories hold that reasoning, categorization, and decisionmaking are the result of two interacting systems, one rule-based/symbolic and the other statistical/associative. The deliberative (Type 2) process is open to introspection but the intuitive (Type 1) is not.

Which system dominates varies by situation. Intuitive reasoning dominates when there is low time or interest. It can also dominate deliberative reasoning when the cost of violating intuition appears large.

The general model of interaction between the systems is that intuition and affect operate through positive feedback and the deliberative system attempts to inhibit the intuitive with varying success depending on relative coherence.

While a weak form of this theory is still largely accepted as useful, there is much criticism based on the difficulty of cleanly isolating the processes. The theory seems to be fading in popularity in favor of multimodularity. The main counter-theory seems to be that deliberative reasoning is mainly cycles of intuitive process.