Prerequisite Tree

The Prerequisite Tree (PRT) is one of the logic-tree tools in Goldratt’s Thinking Processes, the diagramming suite the Theory of Constraints uses to plan a change. As described in the standard ToC literature, it helps work out how to reach a chosen goal by laying out the path from the present situation to that goal.

You build a PRT by listing the obstacles standing between you and the goal, then, for each obstacle, naming the intermediate objective that overcomes it. Because some objectives can only be pursued after others are met, the obstacles and objectives are ordered by dependency, producing a tree of necessary conditions. This turns a vague ambition into a concrete sequence: first clear this, which enables that, which finally permits the goal.

In the ToC toolkit the PRT sits among the logic trees: a Current Reality Tree diagnoses present problems, the Evaporating Cloud dissolves a core conflict by exposing a mistaken assumption, a Future Reality Tree checks that a proposed solution actually yields the wanted effects, and the Transition Tree specifies the step-by-step actions. The PRT bridges solution and execution: it identifies which obstacles must fall and in what order, leaving the detailed action plan to the Transition Tree.

CF treats ToC’s thinking tools as practical aids that complement Critical Rationalism’s emphasis on problem solving and error correction. Elliot Temple’s own introduction to ToC does not name the PRT specifically; it discusses the broader change methodology and the use of trees and diagrams to aid thinking. In CF the PRT rounds out a planning toolkit aimed at achieving goals by focusing effort on the real obstacles instead of unimportant details.