Manufacturing ERP Software
The Thinking Processes Part 1

The Thinking Processes Part 1

By Bob Sproull

What Are the Thinking Processes?

In a nutshell, the Thinking Processes comprise a suite of five logic diagrams as well as a set of logic rules.  As I’ve written about in previous posts, there are three basic questions we should always ask when trying to improve our organization.

- What to change?
- What to change to?
- How to cause the change to happen?

The TOC Thinking Processes are designed to answer these three questions in a very systematic and logical way by exploring and communicating information and assumptions about the current reality and the future reality and how to get there.  Each Thinking Process diagram includes the use of a particular type of logic when they are used.  Some use necessity based logic and some use sufficiency based logic.  So before we delve into each of these tools, let’s first explain the difference between these two different types of logic.

Necessity-Based versus Sufficiency-Based Logic

Necessity-based logic diagrams are those that identify conditions that are necessary for a particular effect to exist.  A sufficiency-based logic diagram is one that identifies all of the conditions that are necessary and sufficient to cause a particular effect. 

While both sufficiency- and necessity-based logic rely on cause/effect relationships, there is a difference between the two.

When testing for sufficiency we ask: “If A occurs, then is this sufficient to cause B?” That is, are the entities within the logic tree complete and valid?

On the other hand, necessity-based logic is looking for those things that must be done to overcome potential obstacles to achieving a particular outcome. These injections (actions or ideas) then become minimum mandatory requirements for the predicted outcome to happen.

Necessity based logic is triggered by asking: “In order to have A we must have B because C”   

For example, In order to minimize downtime at the system constraint, we must plan 100% all equipment services (e.g. scheduled maintenance) and repairs (e.g. unscheduled maintenance) because planning reduces wait time and therefore minimizes the mean time to repair.

Examples of Necessity and Sufficiency Based Logic

To say that A is sufficient to cause B means that if A exists, then it guarantees the presence of B.  Using maintenance as an example, if we were to say that “correctly trained maintenance employees” are required to have a “highly reliable manufacturing plant,” then by saying this suggests that correctly trained maintenance employees (A) will guarantee that we have a highly reliable plant (B). This implies that correctly trained maintenance employees would be a sufficient condition for a highly reliable plant.

To test whether this sufficiency statement is actually true, we need to ask this question: “Is there a situation where A is present but B is not?” We naturally know that in reality there are organizations that do have correctly trained maintenance employees but still have low plant reliability due to many other factors like old equipment, incorrect maintenance strategies, replacement parts not available, etc. Because of this, our original statement doesn’t pass the sufficiency-based logic test. There are many other conditions that must exist like correctly trained operators or enough maintenance personnel that are also required to have a highly reliable plant. Therefore the statement ”properly trained maintenance employees are needed for a highly reliable plant” is not sufficient by itself to guarantee a highly reliable plant.

The logic of necessity is to identify the minimum mandatory requirements to achieve the intended objective. Necessary conditions seek to remove ambiguity and be unequivocal. The primary test for necessity asks “‘is it true that the stated requirement must exist in order for the subsequent outcome to occur?”  For example, in order to have a fire, we must have fuel matches and air.  If one of these is removed then a fire cannot happen, so it is a necessity that all three exist.

The Thinking Process Diagrams

Dr. Eli Goldratt is the man responsible for the creation of the first five logic trees listed below and we will discuss the basics of each one in future posts.  The Goal Tree was developed by H. William Dettmer and, for me, it was a clear breakthrough in logical decision making.  I will spend more time on this logic diagram because it’s the easiest to learn and, in my opinion, will help you the most.

  • Current Reality Tree
  • Evaporating Cloud (EC)
  • Future Reality Tree (FRT)
  • Prerequisite Tree (PRT)
  • Transition Tree
  • Goal Tree

A Question to Ponder

Let's say we want to improve the quality of the product we manufacture.  We want to achieve this effect: "The defect rate of our manufacturing operation is less than five percent." Right now the defect rate is nine percent, and our control-chart shows that our manufacturing system is in a state of statistical control.  If you were to devise an improvement plan, which type of logic would you use to develop the plan?

Next Time

In my next post we’ll begin discussing the Thinking Process tools and the correct sequence in which to use them.  As always, if you have any questions or comments about any of my posts, leave a message and I will respond. 

Until next time.

Bob Sproull

Continue to The Thinking Processes Part 2... 




Bob Sproull

About the author

Bob Sproull has helped businesses across the manufacturing spectrum improve their operations for more than 40 years.

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