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A typical phrenology chart depicts the "modules" of the human mind as compartmentalised physical locations in the brain. This literal visualization is perhaps best viewed as a metaphor for a cognitive (ie. conceptual) view of modularity, though research has shown certain general faculties to be localized to particular regions.

The concept of modularity is also used in other fields. See modularity.

Modularity of mind is the notion that a mind, at least in part, may be composed of innate structures which have established evolutionarily-developed functional purposes (ie. "modules"). Proponents believe this view is implied by Noam Chomsky's concept of a universal, generative grammar. Such features of language imply there's an underlying "language acquisition device" structure in the brain. This device is postulated to be autonomous and specialized for learning language rapidly; a module.

Historically, questions regarding the functional architecture of the mind have been divided into two different theories of the nature of the faculties. The first can be characterized as a horizontal view because it refers to mental processes as if they are interactions between faculties; such as memory, imagination, judgement, and perception; which are not domain specific (e.g., a judgement remains a judgement whether it refers to a perceptual experience or to the comprehension of language). The second can be characterized as a vertical view because it claims that the mental faculties are differentiated on the basis of domain specificity, are genetically determined, are associated with distinct neurological structures, and are computationally autonomous.

The vertical vision goes back to the 19th century movement called phrenology and its founder Franz Joseph Gall, who claimed that the individual mental faculties could be associated precisely, in a sort of one to one correspondence, with specific physical areas of the brain. Hence, someone's level of intelligence, for example, could be literally "read off" from the size of a particular bump on his posterior parietal lobe. This simplistic view of modularity has, of course, been disproven over the course of the last century.

However, Jerry Fodor, drawing from Chomsky and other evidence from linguistics as well as implications from optical illusions and philosophy of mind, revived the idea of the modularity of mind, without the notion of precise physical localizability of the mental faculties, in the 1980s and became one of the most articulate proponents for it with the 1983 publication of his monograph Modularity of Mind.

According to Fodor, a module falls somewhere between the behaviorist and cognitivist views of lower level processes.

Behaviorists tried to replace the mind with reflexes which Fodor describes as encapsulated (cognitively impenetrable or unaffected by other cognitive domains) and non-inferential (straight pathways with no information added). Low level processes are unlike reflexes in that they are inferential. This can be demonstrated by poverty of the stimulus arguments in which the proximate stimulus, that which is initially received by the brain (such as the 2d image received by the retina), cannot account for the resulting output (for example our 3d perception of the world) thus necessitating some form of computation.

In contrast, cognitivists saw lower level processes as continuous with higher level processes in there being inferential and cognitively penetrable (influenced by other cognitive domains such as beliefs). The latter is untrue of lower level processes. For example consider illusions, ex. Mueller-Lyer illusion, that can persist despite a person’s awareness of their existence. This is taken to indicate that other domains, including one’s beliefs, cannot influence such processes.

Fodor arrives at the conclusion that such processes are inferential like higher order processes and encapsulated in the same sense as reflexes.

Although he argued for the modularity of 'lower level' cognitive processes in Modularity of Mind he also argued that higher level cognitive processes are not modular since they have dissimilar properties. The Mind Doesn't Work That Way, a reaction to Steven Pinker's How the Mind Works, is devoted to this subject.

Fodor (1983) states that modular systems must - at least to "some interesting extent" - fulfill certain properties:

1. Domain specificity, modules only operate on certain kinds of inputs – they are specialised
2. Informational encapsulation, modules need not refer to other psychological systems in order to operate
3. Obligatory firing, modules process in a mandatory manner
4. Fast speed, probably due to the fact that they are encapsulated (thereby needing only to consult a restricted database) and mandatory (time need not be wasted in determining whether or not to process incoming input)
5. Shallow outputs, the output of modules is very simple
6. Limited inaccessibility
7. Characteristic ontogeny, there is a regularity of development
8. Fixed neural architecture.

Other perspectives on modularity come from evolutionary psychology, particularly from the work of Leda Cosmides and John Tooby. This perspective suggests that modules are units of mental processing that evolved in response to selection pressures. On this view, much modern human psychological activity is rooted in adaptations that occurred earlier in human evolution, when natural selection was forming the modern human species.

In contrast to modular mental structure, some theories posit domain-general processing, in which mental activity is distributed across the brain and cannot be decomposed, even abstractly, into independent units. A staunch defender of this view is William Uttal, who argues in The New Phrenology (2003) that there are serious philosophical, theoretical, and methodological problems with the entire enterprise of trying to localize cognitive processes in the brain. Part of this argument is that a successful taxonomy of mental processes has yet to be developed.

• Modularity
• Society of Mind which proposes the mind is made up of agents

• Fodor, Jerry A. (1983). Modularity of Mind: An Essay on Faculty Psychology. Cambridge, Mass.: MIT Press. ISBN 0-262-56025-9
• Uttal, William R. (2003). The New Phrenology: The Limits of Localizing Cognitive Processes in the Brain. Cambridge, Mass.: MIT Press.

• Barrett, H. C., and Kurzban, R. (2006). Modularity in cognition: Framing the debate. Psychological Review, 113, 628-647. Full text