[…] what is needed is the following rule: (26) [+—NP⁀Manner] → [+—NP] to be interpreted in the following manner: if (D, C) is a lexical entry with distinctive feature matrix D and complex symbol C containing [+—NP⁀Manner], then C is replaced by C', which contains each specified feature [αF] of C, where F≠ [—NP], and also the specified feature [+—NP] [...] (27) [+—φ⁀Manner] → [+—φ]. This is to be interpreted as follows: first, select any constant string as φ; second, interpret the result in the manner described in connection with (26) [...] (28) (i) ("walk", [+—Manner,...]); (ii) ("hit",[+—NP⁀Manner,...]) [...] Rules such as (27), (28) are closely analogous to the phonological rules that Halle called "morpheme structure rules" (Halle, 1959a, 1959b) [Halle, M. 1959a. “Questions of linguistics”, Nuovo Cimento, 13, pp. 494-517; -1959b. The Sound Pattern of Russian. The Hague: Mouton], and that I have been referring to here (following a suggestion of his) as "phonological redundancy rules" [...] The redundancy rules, both phonological and syntactic, state general properties of all lexical entries, and therefore make it unnecessary to provide feature specifications in lexical entries where these are not idiosyncratic [...] Given a lexical entry ("D, C"), the phonological redundancy rules give a fuller specification to "D" [...] The real function of the phonological redundancy rules is to determine the class of the phonological admissible (though perhaps nonoccurring) sequences in a principled way.
- Chomsky (1969), a pag.167-169