TRIPLETS, QUADRUPLETS, AND MORE

You may notice that not all project management writers describe the triple constraints in the same way, and some do not reference the triple constraints at all. The term “triple constraints” does not appear in the PMBOK® glossary or index. Sometimes writers will identify additional constraints, and you’ll have four or five. Performance is sometimes referred to as “scope” or “quality,” and “cost” and “resources” are often listed separately.

There’s more than one way to skin a cat, of course, and the particular arrangement chosen by an author or trainer is often related to the learning point at issue. The particular view of the triple constraints presented here has several advantages:

It’s a classic interpretation, focusing on the “big three” without adding or subdividing.

The model accounts for all the other issues that have been raised with respect to the triple constraints, such as the role of customer relations and non-cash resources.

It makes clear some important distinctions, such as the difference between performance and quality.

Of course, models by their very nature are neither true nor false, but rather are useful or not useful. More than one model can be of use or can illustrate a different part of the puzzle. Let’s look at some of the other interpretations of the triple constraints.