As I have mentioned here before, I am working on a third edition of Machinery. My current plan is what I did for the second edition—leave the existing text alone aside from minor changes and simply add a new section with the new material.
My question is whether that is a good idea or whether I should attempt the more difficult task of rewriting the whole thing. The argument against is that the original was not really about the world in 1972; the logic of what I was doing was intended to apply much more generally than that. My views of some issues have deepened but not substantially changed. And the original seem to have worked for a good many readers. If it isn't broke, why fix it?
Also, I'm lazy.
The argument the other way is that a good deal of the new material relates to parts of the old. There is a chapter in the first edition on the problem of producing national defense without a government. There is another chapter on that subject that will be in the third edition. I could try to combine them into one chapter.
Similarly, in the first edition I discussed the question of what the defining characteristic of a government was, how we distinguish governments from other institutions, given that pretty nearly every function performed by a government has also been performed, at some time and place, by something that isn't a government. My conclusion was that a government was an agency of legitimized coercion, with special definitions for both "legitimized" and "coercion." In the third edition I fill out that argument by asking how and in what sense any society can get out of the Hobbesian state of nature, offering an answer involving commitment strategies and Schelling points, and using that answer to more clearly explain what I meant by coercion and legitimized, hence what is special about a government.
I see three possible alternatives for dealing with such situations. One is to combine two chapters into one, eliminating some of the old material in the process. One is my present plan, a part V containing all the new material. An intermediate possibility is to retain the old material but intersperse it with the new, putting the new chapter on national defense immediately after the old, and similarly with the chapter on defining government.