Hanging on a wall in my office is a poster that diagrams a 958-word stretch of text from French author Marcel Proust's Cities of the Plain. The label on the poster claims it is the longest sentence.
It is not the longest sentence anyone has written; it is not the longest sentence anyone could write, but that is another issue.
The issue we are concerned with is the usefulness of the diagram. It is not very useful but it is much admired. The Reed-Kellog diagram that outlines Proust's sentence, with lines going off every which way to fill the 3'x5' poster, is marveled at by almost everyone who comes into my office for the first time. "wonderful," some say, or "I wish I could do that." They are wrong to value the diagram so much. ... The poster has so many lines that it is useless as a visual aid. ... It is complicated and intimidating.
The point to remember about diagramming is simple: if it helps you to visualize the structure and function of constituents, use diagrams. But do not get too caught up in them;
no diagramming system will help when sentences become much more involved than those we are analyzing in these first few chapters. And diagramming is neither a virtue nor a central goal of grammatical analysis. Diagramming is at best a tool that can sometimes help you visualize constituents and their relationships. Diagrams are tools, not goals.
The goal of grammatical analysis is to recognize constituents, hierarchies, relationships.