Where does modularity collide?

The design of a product or system as a set of largely independent modules that connect through standardized interfaces, so that each module can be built, changed, or replaced with little effect on the others. Ulrich's 1995 The role of product architecture in the manufacturing firm tied this to how a product's functions are mapped onto its physical components, and Baldwin and Clark's 2000 Design rules: The power of modularity treated modular design as a source of strategic flexibility and industry structure. Here modularity is a property a designer builds into an artifact, judged by how cleanly the components separate, and it is different from a computed score on a network, a biologist's semi-independent body parts, or a philosopher's account of the mind.[1][2]

Unit

A product decomposed into modules joined by defined interfaces

Recovery means

Not applicable

Measured by

Judged by how standardized the interfaces are and how independently one component can change without forcing changes in others

A single number that measures how well a network splits into communities, comparing the fraction of links that fall inside groups against what would be expected if the same links were placed at random. Newman and Girvan's 2004 Finding and evaluating community structure in networks introduced this quantity, and Newman's 2006 Modularity and community structure in networks showed how to find the grouping that makes it as large as possible. Here modularity is a computed quality of a particular partition, high when a grouping captures real structure, and it is not a design property of a product, a feature of an organism, or a claim about the architecture of the mind.[3][4]

Unit

A dimensionless score, roughly between 0 and 1, for a given partition of a network

Recovery means

Not applicable

Measured by

Computed as Q, the within-group link fraction minus its random expectation, then maximized over possible partitions

The organization of an organism into units, whether developmental, genetic, or anatomical, whose parts are tightly connected within a unit and only loosely connected between units, so that each unit can vary and evolve somewhat on its own. Wagner and Altenberg's 1996 Perspective: Complex adaptations and the evolution of evolvability argued that such a modular map from genes to traits makes a lineage more able to adapt, and Wagner, Pavlicev, and Cheverud's 2007 The road to modularity reviewed the evidence for it. Here modularity describes how a living body is partitioned into quasi-independent parts, inferred from patterns of variation, and it is separate from a designed product, a network score, or a theory of the mind.[5][6]

Unit

A body or a genotype-to-phenotype map partitioned into quasi-independent units

Recovery means

Not applicable

Measured by

Inferred from correlation patterns among traits and from developmental and genetic dependencies among parts

The claim that the mind contains special-purpose systems, each dedicated to a narrow task such as recognizing faces or parsing speech, that work quickly and automatically and cannot be freely steered by the rest of what a person knows. Fodor's 1983 The modularity of mind set out these features, including domain specificity and what he called informational encapsulation, the way such a system is sealed off from general knowledge. Here modularity is a proposed feature of how the mind is built, argued from behavior and from brain injury, and it does not name a designed product, a network score, or the evolving parts of a body.[7]

Unit

A hypothesized mental system dedicated to one kind of input

Recovery means

Not applicable

Measured by

Argued from selective deficits after brain injury, from fast automatic processing, and from resistance to what a person otherwise knows