An approach in financial economics that incorporates psychological insights about heuristics, biases, emotions and social preferences to explain observed deviations from normative financial models and market anomalies.

Principle

Systematic cognitive biases and heuristics at the individual and institutional level can produce predictable departures from models based on fully rational agents, affecting prices, trading patterns and allocation of capital when arbitrage is limited or costly.

Demonstration

Illustrative scenario → Situation: Repeated surprising news causes investors to overreact. Recognition → Traders notice persistent price momentum inconsistent with fundamentals. Action → Some investors exploit momentum while others follow herding behavior; limited arbitrage prevents immediate correction. Consequence → Temporary mispricings and momentum returns that are better explained by behavioral mechanisms than by instantaneous incorporation of fundamentals.

Misapplication

Invoking behavioral explanations as the default causal story for any anomaly without testing alternative explanations (institutional frictions, data issues, rational learning) and without specifying which cognitive mechanism is implicated.

Consequence

Leads to revised asset‑pricing models, improved understanding of market anomalies, design of behavioral interventions (disclosures, choice architecture), and attention to limits of arbitrage in market regulation and portfolio construction.

Reversal

When arbitrage is effective and frictions are low, psychological biases may be arbitraged away and classical rational models (e.g., efficient markets) regain predictive power; some anomalies vanish with improved information or market structure.

Boundary

Within: explanations that foreground psychological mechanisms (biases, heuristics, sentiment) as causal contributors to financial outcomes. Near edge: institutional or informational explanations that interact with psychology. Outside: purely neoclassical models that assume fully rational agents and frictionless markets.

Semantic Tension

Psychology‑based explanations of market outcomes ↔ Classical efficient‑market models; both offer constraints and may apply under different assumptions about frictions and aggregation.

Synthesis

Behavioral finance supplements rather than simply replaces classical finance: it identifies when and how psychological mechanisms, combined with market frictions, produce systematic patterns that normative models alone do not predict.