Extended Mind

Extended Mind (Extended Mind) thesis is an approach that argues cognitive processes do not occur solely within the individual’s brain or biological body, but that under appropriate conditions, external objects and tools can also serve as constitutive elements of cognition. This view was first proposed by Andy Clark and David Chalmers in 1998.^【1】 The thesis has rekindled the question of how to define the boundaries of the mind by bridging philosophical theories of the mind with cognitive science.

Historical and Theoretical Background

Traditional philosophy of mind approaches have held that mental states and cognitive processes are confined to the individual’s internal structure, especially the brain. This view is commonly referred to as internalism. However, from the second half of the 20th century onward, functionalism began to define mental states by their functional roles rather than their physical locations. This shift opened up debate about whether cognition is confined to the brain.

In this context, embodied cognition and situated cognition approaches have argued that mental processes are shaped through interaction with the body and environment. The Extended Mind thesis builds on these approaches by asserting that environmental elements are not merely influences on cognition but can be direct constituents of it.

The Extended Mind Thesis

Clark and Chalmers’ central claim is that in explaining cognitive processes, the “skin and skull boundary” should not be granted privileged ontological status.^【2】 They argue that if an external entity performs the same functional role as a cognitive process typically assumed to occur in the brain, there is no strong reason to exclude it from the cognitive system. This idea is expressed through the parity principle. According to this principle, if an internal process is recognized as cognitive, an external process performing the same function should not be excluded from being cognitive merely because of its location. The criterion is not where the process occurs but its functional role within the cognitive system. Clark and Chalmers also emphasize that not every external tool automatically becomes part of cognition. They therefore propose specific conditions for cognitive extension: the tool must be reliably accessible, consistently used, automatically invoked, and epistemically trusted by the user. When these conditions are met, external tools are not merely aids but can be regarded as constitutive elements of cognition.

Classic Examples and Thought Experiments

The most discussed example of the Extended Mind thesis is the thought experiment involving Otto and Inga. Inga remembers the address of a museum from her biological memory when she wishes to visit it. Otto, who suffers from Alzheimer’s disease, regularly writes information in a notebook. When he needs to know the museum’s address, he consults his notebook and acts on the information. According to Clark and Chalmers, Otto’s notebook plays the same functional role as Inga’s biological memory. In both cases, information functions as a reliable source guiding behavior. Therefore, Otto’s notebook should be considered part of his cognitive system. This example aims to show that mental states such as memory, belief, and knowledge do not have to occur solely within the brain. Today, agendas, navigation apps, and smartphones can be understood in similar terms.

Cognitive Artifacts and Technology

The Extended Mind approach places cognitive artifacts at the center of its analysis. Writing, mathematical notation, diagrams, maps, and digital devices are seen as tools that reduce cognitive load and structure cognitive processes. Clark argues that these tools do not merely store information but also reshape the very form of cognitive processes. He therefore labels them “cognitive scaffolds.” In particular, language plays a fundamental role in extending cognition into the environment. Through language, cognitive processes can be distributed across social and cultural structures.

Critiques and Objections

One major criticism of the Extended Mind thesis is that it blurs the distinction between interaction and constitutive involvement. Cappelen and Dever acknowledge that many external tools interact with cognitive processes but argue that this interaction does not automatically entail that these tools are parts of cognition.^【3】 Another criticism is the “cognitive bloat” problem: if every reliable and accessible tool counts as part of cognition, the boundaries of the mind could expand excessively, rendering the concept analytically useless.