Full Idea
There are four kinds of reduction: the identifying of entities of two theories by means of bridge or correlation laws; the elimination of entities in favour of the other theory; reducing by bridge laws and property identities; and merely reducing talk.
Gist of Idea
Reduce by bridge laws (plus property identities?), by elimination, or by reducing talk
Source
Cynthia Macdonald (Varieties of Things [2005], Ch.3 n5)
Book Reference
Macdonald,Cynthia: 'Varieties of Things' [Blackwell 2005], p.123
A Reaction
[She gives references] The idea of 'bridge laws' I regard with caution. If bridge laws are ceteris paribus, they are not much help, and if they are strict, or necessary, then there must be an underlying reason for that, which is probably elimination.