Why MECE is not complete

Introduction

Those who have been in the consulting world will have heard of the MECE principle. This stands for "mutually exclusive, collectively exhaustive". It is one of the foundations of Barbara Minto's Pyramid Principle, a way of structuring your writing in business in a more concise and comprehensible manner. MECE refers to how you should divide your set of arguments to best support your hypothesis.

MECE

Mutually exclusive means that each argument should be self contained and not encroach in the space of another argument. For example, if I'm talking about why you should modernize your IT estate, one argument could be that it provides a better customer experience, while another argument could be that it reduces costs. These two arguments have nothing in common with each other. However, if one argument is that it provides a better customer experience, another argument cannot be that it reduces IT outages. There is too much overlap between these two arguments and they are not mutually exclusive of each other. Instead reducing IT outages should be a sub-argument that supports the better customer experience argument and not an argument in its own right.

Collectively exhaustive means that all the known arguments should be stated. In our previous example of modernizing your IT estate, the arguments could be that it enables business agility, improves customer experience, reduces costs, and maintains compliance with regulations. Almost all other arguments could be classified as a sub-argument of one of these arguments. Therefore, this set of four arguments is collectively exhaustive.

Categorically Expectant

While MECE sounds like a sound approach to structuring your arguments, it is not as complete as it should be. In the previous paragraph with the example of modernizing your IT estate, if I added "it will make the sun seem brighter" as an argument, my arguments would still be MECE. However, this last argument should not be there as it has nothing to do with IT modernization.

To rectify this, I'd like to introduce an additional term: categorically expectant. In other words, the arguments as a set should not contain anything that is not expected within the set, thus MECE becomes MECECE. If I list the Three Musketeers, I'd include Athos, Porthos, and Aramis. If I added Cinderella into this list of the Three Musketeers, my list would still be MECE, but not MECECE.

Closing thoughts

MECECE is arguably a better approach to structuring your arguments than just MECE is. Mutually exclusive ensures there are no overlaps in your arguments. Collectively exhaustive ensures there are no gaps in your arguments. And categorically expectant ensures there are no errant scraps in your arguments.