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The Thinking Process is the problem solving method of TOC. It is a suite of tools for finding the root cause and driving the improvement.

The principle

The thinking processes is a set of tools, used throughout the continuous improvement process, advocated by Goldratt to answer the three questions1 :

  1. What to change?
  2. What to change?
  3. How to make change happen?

The thinking processes constitutes a set of a series of logical tools composed of entities structured in trees and linked together by arrows signifying, as the case may be, a necessary condition or a sufficient condition.

Thinking Process logic

Based on scientific reflections, the tools of the thinking Process respond to the classical causal logic of Mathematics: “If…,” “then… ».

Logic of the necessary condition

By definition, a condition B is a necessary condition of a if and only if the falsity (inexistence and absence of occurrence) of B guarantees the falsity (inexistence and absence of occurrence) of a.

For example :

  • “To make an omelette, it is necessary that I break eggs”.
  • The “Break eggs” condition is called a necessary condition.

Logic of Sufficient condition

By definition, a condition A is a sufficient condition of B, if and only if the truth (existence or occurrence) of has guaranteed the truth (existence or occurrence) of B.

For example :

  • to make an omelet just break eggs. »
  • The “Make an omelet” condition is called a sufficient condition.

The overall process of the Thinking Process

The Thinking Process consists of 5 separate logical trees to help with the logical reflection required to answer the questions mentioned above2. The Thinking Process first identifies the symptoms of the problem. The tools are then used for ” deduce the causes of these symptoms “(question 1),” what needs to be done to correct these causes “(question 2), and” how these corrective actions can be implemented (question 3), in accordance with strict rules of logic and the rigour of the reflection of causes and effects3.

Process Tree Logic
Question 1: What to change? 1-Tree of the present reality Sufficient Condition
Question 2: What to change?

2-Evaporating Cloud

3-Future Reality Tree

Necessary Condition

Sufficient Condition

Question 3 How do I change?

4-Prerequisites Tree

5-Transition Tree

Necessary Condition

Sufficient Condition

The rules

All the trees are constructed from acronyms (rectangle with rounded edge, rectangle at right angles…) representing the reality, an action…

The entities are connected to each other by oriented arrows. The direction of the arrow given according to the logic of the necessary condition or sufficient condition.

The logical robustness of the built trees has been tested by the CLR (Categories of Legitimate Reservation – Legitimate reserve category) which allow to verify the entities composing the trees, by the editor (s) of the tree or better thanks Non-editors.

The different acronyms and arrows

Entities: They consist of a complete sentence (subject, verb, object) in the present. They describe the present reality of an effect or a cause.

Injection or condition: this is a necessary action that does not exist in the present and will allow the change. In the same way as the entities, they are made up of complete sentences in the present.

It indicates the existence of a conflict between 2 conditions or prerequisites at the lowest level of its appearance.

Each entity is connected by arrows. The base of the arrow leaves the cause and points to the effect for the trees with sufficient conditions and in reverse for the trees with necessary conditions.

It is an obstacle that prevents the execution of an injection or a goal. It is exceeded by an intermediate objective represented by a rectangle.

Called connectors, it is used when multiple entities can be the cause of an effect, the ellipse being used to link the arrows.

CLR-Legitimate Reserve Category

The logical robustness of the trees is based on the robustness of the written entities and the logical test of the links between all the components of the trees.


The objective is to question the clarity of information. You have to ask yourself a question:

  • is the entity expressed in a clearly understandable manner?
  • is the meaning and context unambiguous?
  • The relationship of cause and effect to a true value?

Entity existence (the existence of the entity)

The objective is to question the reality of information and its existence in the present. You have to ask yourself a question:

  • Does the expressed entity really exist in reality?
  • Can it be documented easily?

Causality existence (the existence of causality)

The objective is to question the logic between 2 connections of cause and effect. You have to ask yourself a question:

  • Is there really a cause-and-effect relationship (if…, then) between the two entities?
  • In the proposed cause, the result is not given?
  • Does it make sense when you say it out loud?
  • Is the cause intangible?

Cause insuffiency (lack of cause)

The objective is to question whether it is not lacking an important cause, and thus have “if.. . And if…, then… “. You have to ask yourself a question:

  • Does the cause as described justify the whole effect?
  • is the entity sufficient to produce the predicted effect?
  • Are there other underlying causes that are not present?

Additional cause

The objective is to question whether there are several causes that do not cause the same effect. You have to ask yourself a question:

  • Is the proposed additional cause necessary to produce the predicted effect?
  • If the cause is eliminated, is the effect really suppressed?

Cause-effect reversal (inversion of the causal relationship)

The objective is to question whether the meaning of the cause-effect relationship is not reversed. You have to ask yourself a question:

  • The cause induces it the effect or is the reverse?
  • is the cause well the first cause or just a way to justify the effect?

Predictated effect Existence

The objective is to question the existence of the effects and their prediction. You have to ask yourself a question:

  • Does the predicted effect exist in reality?
  • The cause is intangible?
  • Can the same cause be responsible for other effects?

Tautology or reversal reservation

The objective is to question whether the cause is indeed that of the effect and not the other way around. You have to ask yourself a question:

  • Is the cause intangible?
  • Is there a circular relationship between cause and effect?

The Five Trees

1-Current Reality Tree (CRT)

The Current reality Tree (CRT) allows you to answer question 1 “What to change?”, and thus to find the root cause to the problems encountered.

It is built in the following way:

  1. List the side effects with the entity acronym. It is generally recommended to start with 5 to 10 maximum effects5.
  2. Link the adverse effects of the cause (s) identical to each other.
  3. Reassemble the tree in the logical effect-cause sufficient until reaching the first cause.
  4. Put the different constraints.
  5. Connect through the ellipses the causes that are the sources of the same effect.
  6. Reread the tree by asking if it matches your intuition and if it follows the logic “If <entity> and if <entity> then <entity>“.
  7. Check the tree using CLR criteria.
  8. Identify the most common cause of the various adverse reactions, which is the cause of minimum 70% of the problem.

2-Evaporating Cloud (EC)-Conflict resolution diagram

The Evaporating Cloud (EC), a conflict resolution diagram, is used to generate ideas to help resolve hidden dilemmas and conflicts that cause a fundamental problem. It allows to answer the first part of the question “Change for what?”. It is based on two postulates:

  • Most conflicts are resolved by a compromise.
  • Many conflicts find their origins on assumptions, beliefs… false.

It is built in the following way:

  1. Identify the purpose of the problem (the kernel of the problem in the previous tree).
  2. Identify the necessary requirements.
  3. Identify the necessary prerequisites.
  4. Identify the conflict between two possible solutions.
  5. Make sure that conflict solutions have an impact on the problem.
  6. Find the ” injections ” necessary for the functioning of the solutions.
  7. Compromise and find the best solution.
  8. Check the tree using CLR criteria.

3-Future Reality Tree (FRT)- Tree of the future

It is the visual representation of the future of causes and effects. The Future Reality Tree (FRT) serves two purposes:

  • It makes it possible to verify that the action to be implemented will produce the expected results.
  • Identify possible new adverse consequences to eliminate them and validate the feasibility of the solution.

It is built in the following way:

  1. From the injection identified in the EC
  2. Connect the injection to desirable effects in the logic of sufficient condition
  3. Go back up until you reach the solution as defined in the previous tree.
  4. Create a “ negative branch ” (called NBT: Negative branch Tree): The challenge is to identify the negative consequences of the potential solution. In the same way, one starts from the injection and the tree is traced by identifying the side effects.
  5. Check the tree using CLR criteria.
  6. Finally, you can conclude on the solutions (injection) to implement, corrective actions to prevent the unfortunate consequences and a loop to perpetuate the actions. If you can’t bypass or identify an injection that removes the negative branch, you need to find another solution and go back to the previous step.

4-Prerequisite tree (PRT) or pre-requisite tree

The prerequisite Tree (PRT) is an aid to the execution of actions to be implemented by identifying the intermediate obstacles to overcome that constitute successive objectives (called IO ” Intermediate objective “).

It is built in the following way:

  1. Start with previously validated “injections”
  2. Identify the various intermediate steps (IO) to achieve the goal according to the logic of the necessary condition.
  3. Between each IO, define the obstacle (or obstacles) to achieve it.
  4. Check the tree using CLR criteria.
  5. Identify the different obstacles to be passed.

5-Transition Tree (TT)

The last of the 5 tools is the Transition Tree (TT). It established the roadmap to the detailed objectives previously. ” injections ” are transformed into real actions to allow for change.

It is built in the following way:

  1. Start with the previously identified obstacle (IO).
  2. Put the condition in the present reality that explains why this action satisfies our need.
  3. Identify the action (Initiator’s actions) that allows to pass the obstacle: it usually flows from ” injections ” but are representative of actions in the reality of context.
  4. Ask the question, ” why the first action could prevent the negative consequences of the next action “.
  5. Check the tree using CLR criteria.

Global view of the process


1 – Mr. E. Goldratt (1994)-It’s not luck, Gower

2 – H. W. Dettmer-(2007)-The Logical thinking Process: A Systems Approach to complex Problem Solving

3 – S. Kim, V.J. Mabin, J. Davies (2008)-The Theory Of constraints thinking Processes: Retrospect and Prospect

4 – H. W. Dettmer (1997)-Goldratt’s Theory of constraints: A Systems Approach to Continuous


5 – S. Rahman (2002) – The Theory of constraints, thinking process approach to developing growth strategies in supply chain

V. Von, S. S. Asan (2009) – A methodology based on Theory of constraints ‘ thinking processes for managing complexity in the Supply Chain

T. Louafa, F. L. Perret (2008) – Creativity and innovation: collective intelligence in the service of management

J. H. Goh (2009) – The Tree of Reality presents

F. A. Meyer (2014) – Apply the ToC Lean Six Sigma in the services

H. W. Dettmer (2003) – Strategic Navigation: A systems approach to business strategy



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