The Mental Models Global Laboratory is a consortium of scientists, scholars, professors, and students who conduct and report studies on the strengths and failures of human reasoning. We focus investigating the psychology of reasoning by conducting basic research running laboratory experiments and developing computational models of higher-level cognitive processes. The webpage was set up, and continues to be maintained, by Sunny Khemlani (skhemlani@gmail.com).

Experimental data in cognitive psychology suggest that humans reason and solve problems through the use of internal representations that can be mentally scrutinized and processed — mental models. The theory that posits the existence of such models and the mechanization thereof, known as mental model theory, was established by Phil Johnson-Laird (1983) and has proven extremely powerful in predicting and explaining higher-level cognition in humans.

“Deduction is that mode of reasoning which examines the state of things asserted in the premisses, forms a diagram of that state of things, perceives in the parts of the diagram relations not explicitly mentioned in the premisses, satisfies itself by mental experiments upon the diagram that these relations would always subsist, …and concludes their necessary, or probable, truth.”
– Charles Sanders Peirce

The theory departs from the view that humans reason by implementing a logical or a probabilistic calculus. “Formal rules of inference play no part in inferences,” says Johnson-Laird, “though from Piaget onwards, psychologists have proposed theories based on them.” Instead, proponents of the model theory argue that people reason on the basis of possibilities — what makes reasoning difficult, in part, is the computational inability to consider all relevant possibilities at once. People need to consider one possibility at a time, and often the first one that comes to mind suffices. So, people make mistakes.