 Informational encapsulation is related to what Pylyshyn (1984, 1999) calls cognitive impenetrability. But the two properties are not the same; instead, they are related as genus to species. Cognitive impenetrability is a matter of encapsulation relative to information stored in central memory, paradigmatically in the form of beliefs and utilities. But a system could be encapsulated in this respect without being encapsulated across the board. For example, auditory speech perception might be encapsulated relative to beliefs and utilities but unencapsulated relative to vision, as suggested by the McGurk effect (see below, §2.1). Likewise, a system could be unencapsulated relative to beliefs and utilities yet encapsulated relative to perception; it’s plausible that central systems have this character, insofar as their operations are sensitive only to post-perceptual, propositionally encoded information. Strictly speaking, then, cognitive impenetrability is a specific type of informational encapsulation, albeit a type with special architectural significance. Lacking this feature means failing the encapsulation test, the litmus test of modularity. But systems with this feature might still fail the test, due to information seepage of a different (i.e., non-central) sort.