[...] a MS rule consists of two parts: a STRUCTURAL DESCRIPTION SD(R) and a STRCTURAL CHANGE SC(R). SD(R) and SC(R) may be thought of as being a pair of incompletely specified, disjoint matrices with the same number of columns. The kind of matrices we are concerned with here have entries "+", "-", or no entry (blank), and have a fixed number n of rows, each of which will correspond in an actual grammar to a distinctive feature.
- Stanley (2004), a pag.62

[...] all the phonological redundancy rules of the grammar are stated in a single separate set of rules, the MS rules, which predict all phonological redundant information before either the transformational rules or the P rules apply [...]. The P rules may change feature values (that is, change a minus to a plus or a plus to a minus), they may add or delete whole segments, and they permute segments. The MS rules, on the other hand, must not do any of these things; their sole function is to fill in blank entries with the proper values ("+" or "-"), for, as noted, they are exclusively redundancy rules.
- Stanley (2004), a pag.48

[...] MS rules can be replaced by a new device, MS CONDITIONS [...]. MS rules and MS conditions are very similar. In particular, we can talk about segment structure CONDITIONS and sequence structure CONDITIONS in the same way that we talked about the corresponding kinds of RULES.
- Stanley (2004), a pag.75-76

In some sense the MS rules were viewed as redundancy rules, but this fact was not emphasized, and the distinction between redundancy rules and feature-changing rules played no real role.
- Stanley (2004), a pag.47