This article is about my research into the structure of what we say when we write or speak. Many years ago, while teaching a course on technology and public policy at Carnegie Mellon, I discovered a logical form that underlies the discussion of complex issues. This logical form had a branching structure so I called it the “issue tree.”
Since then I have done a lot of research on issue trees, as well as using diagrams of them to help my clients deal with complex issues. Knowing that issue trees exist whenever we talk or write can be helpful so I will explain the basics here. For those who want to know more I have a crude little textbook on it that I wrote for my own classroom use, entitled “Issue Analysis: an introduction to the use of issue trees and the nature of complex reasoning.” Also, I have already presented the issue tree in a Kitchen article as a model of scientific progress and looking at that graphic may help one understand what I am about to say.
The basic pattern of the issue tree is quite simple. An issue begins when a statement is made (or a question is asked). There can be several immediate responses. The discovery was that statements made in response are answering questions of the initial statement, questions that are typically unspoken. These unspoken questions define precise relations between the statements.
As discussion continues more statements are made, each answering an unspoken question of some specific prior statement. Thus there is a precise branching structure underlying everything that is said. Much follows from this. Note that these component statements may be made by a single person or document or by many, all at once or spread over a long period of time.
By way of example, here is a link to the issue tree underlying the fine print in an automobile loan contract. The textbook has more examples, however it is mostly about how to draw issue tree diagrams. Note that the issue tree and the issue tree diagram are two different things, just as roads and roadmaps are. The issue tree is there when we talk and write, individually or collectively over time, whether we see it or not. This is not just a diagramming technique; rather it is a basic fact about human discourse.
There are some well known indicators that expressed thought has a branching structure. The outline, for example, and the nesting of blog comments are both tree structures. There are also various so-called “mind mapping” techniques. My discovery is that this structure is precise, well defined and universal.
Actually it is not quite this simple because sometimes a statement will refer to a body of prior statements rather that a single one, but that is an advanced topic. The real question is, how is this useful to know?
First and foremost is the fact that when we talk and write we are articulating complex and sophisticated structures, even in the most mundane cases. We are constantly deciding which sentences to respond to and which unspoken questions of those sentences to answer. I start my textbook with a seemingly silly minor argument just to make this point. We are not just piling on statements; rather we are creating systems of ideas.
While the combination of unspoken questions being answered can be a complex structure, the questions themselves are typically very simple. They frequently include the famous who, what, where, when, why and how, as well as “such as” (which is asking for an example) and “what evidence”. If there is disagreement, they will also include objections and replies. The questions are not really there, mind you, unless they are expressly asked; they just represent the specific relations between the statements being made.
Then there is what I call the “jumping problem,” which is a major source of confusion in human communication. Speaking and writing are both linear in the sense that one sentence comes after another, but they are expressing a branching tree structure. The problem is that there is no way to put each sentence directly after the sentence it is linked to and building on. Graphically this means that we are forced to jump around in the issue tree and sometimes these jumps are quite large. The reader or listener must then make the connection back to the prior sentence and this can be difficult, hence the potential for confusion. The jumping problem is discussed in the textbook.
Knowing the issue tree is there creates a new science of sorts because there are a lot of structural features that can be counted and measured in human discourse. These include rates of branching, the allocation of attention to different sub-issues, or to different question types, as well as patterns of jumping. For example meetings tend to have very low branching rates, because it is hard to get back to prior statements. Thus meetings may not be a good way to explore complex issues. Many of the items in my taxonomy of confusions are based on issue tree features.
Issue tree diagrams can be useful in articulating or dealing with complex issues. They have been used to deal with various sorts of issues including strategic planning, decision making, policy and regulatory analysis, litigation, contracting, and system design. But it is important just to know the structure is there whenever you talk, write, read or listen.
On an historical note I first presented the issue tree in a conference on philosophy of technology at the University of Illinois in Chicago Circle in 1973. The proceedings were finally published in 1979 as “The History and Philosophy of Technology,” edited by Bugliarello and Doner, University of Illinois Press. Mine is Chapter 14 entitled “The Structure of Technological Revolutions.” By that time I had left academia for the world of issue analysis and management consulting, but I have continued the research as well.