Dual-process theories propose that human cognition operates through two qualitatively different systems. System 1 (Type 1 processing) is fast, automatic, effortless, and intuitive — it generates impressions, feelings, and inclinations without deliberate effort. System 2 (Type 2 processing) is slow, deliberate, effortful, and analytical — it monitors and (sometimes) corrects System 1's output, performs logical analysis, and handles novel, complex problems. The framework, popularized by Daniel Kahneman in Thinking, Fast and Slow (2011), provides a unifying account of a wide range of cognitive phenomena.
Properties of the Two Systems
System 1 operates automatically and cannot be turned off — it continuously generates impressions, associations, and intuitive judgments. It relies on heuristics, is susceptible to biases, and is contextualized by emotion and personal experience. System 2 is capacity-limited, requiring effort and attention. It is engaged for complex reasoning, self-control, deliberate analysis, and the application of learned rules. System 2 can override System 1, but doing so requires cognitive resources and motivation.
Evidence and Applications
Dual-process theories explain why people can simultaneously know the correct answer and give the wrong one (when System 1 provides a compelling but incorrect intuition that System 2 fails to override), why cognitive load increases reliance on heuristics (System 2 is depleted), and why experts can make rapid, accurate judgments (their System 1 has been trained through extensive experience). The framework has been applied to judgment and decision making, moral reasoning, social cognition, and clinical psychology.
Dual-process theories have been criticized for being too vague (the two "systems" may not be unitary systems but collections of diverse processes), for the difficulty of specifying when System 2 will intervene, and for potentially oversimplifying the continuum of cognitive processes. Some researchers (such as Melnikoff and Bargh) have questioned whether the Type 1/Type 2 distinction maps onto a single, principled divide. Despite these criticisms, the framework remains enormously influential and heuristically valuable.