I try to make all my arguments mutually exclusive and collective exhaustive. M.E.C.E in short. I learned it in consulting. What does M.E.C.E. mean? Its means that I try to avoid individual propositions to overlap between themselves and at the same time I try to address the whole, not a part of it.
One example: When asked to provide an accurate description of a tree, one answer can be “A tree has a trunk, branches and leaves. Upon this brown and green base, you have bright and colourful flowers and fruits.”
We can see that there are at least two problems with this description.
- a trunk, branches and leaves are generally brown and green. Sure. But fruits can be green too. The green is not exclusive to trunk, branches and leaves. And colourful is definitely not exclusive to flowers and fruits. So the description terms as they stand are not mutually exclusive.
- there is no mention of roots. Therefore the collective description is not exhaustive.
The first problem is the violation of mutual exclusiveness (M.E.). It happens when we use mix different classes of attributes to describe the tree. In my example I mixed color and morphology. Why does using different classes break M.E.C.E.? Because if one set of attributes is already collectively exhaustive and covers the whole, then any other different attribute will be overlapping that whole that you just covered and therefore not be mutually exclusive with the first attribute!
To create the example, I just described what came to my mind. If you wanted to do a proper description for your arguments, a M.E.C.E. one, you should instead start picking attributes from available observation points:
- What makes X. In the tree example, we’re talking about the morphology: roots, trunk, branches, etc. We could also pick a more detailed level, like the types of chemical compounds that exist on a tree.
- What does X look like. In the tree example, we can use attributes like color, but also different ones like height, or smell and texture.
- What are the dependencies of X. In this example, it can be the sun, water, nutrients in the soil, or the wind to carry the seeds.
- The evolution of X. For a tree, we’d be talking about the seed stage, sprout, full tree formation, or different seasons.
- The dependents of X. In the example, it could be ashes, another tree, fertiliser, food, carbon. This one is tricky, ok. You get the picture.
Mutual exclusiveness helps you compartmentalise. Why is it good? When you are trying to reach some conclusion with your description, you want each piece of the argument to have standalone credibility. Because even if people challenge one item, that is unlikely to affect others and your conclusion may still hold. In the example above, if you as my listener pointed that some trees have flowers and fruits that are are not at all bright and colourful, then not only would I have to amend it, but also correct the reference of the brown and green trunk and leaves being the color base of the tree relative to the flours and fruits. My whole description just fell apart. Instead if your propositions are mutually exclusive, your job is much cleaner.
The second problem is the violation of collective exhaustiveness (C.E.). It happens when you leave stuff unmentioned. Not mentioning roots makes your description incomplete, as they may be important. And rightly so - of course they are!
Therefore a better description would be: “A tree has roots, a trunk, branches, leaves, flowers and fruits.” This is way much more M.E.C.E. Now, we know that each additional attribute we want to mention will not be M.E.C.E. with the previous ones, but we may want to use them anyway to enrich the argument. Let’s say color. So while we can’t make color M.E.C.E. with morphology, we can at least have the color description be M.E.C.E. within each of the morphology items individually: “Roots are generally brown, and so are trunks and branches. Leaves are green, yellow, red or brown. Fruits can have those same colours. Flowers too, but also white, purple, and pretty much all colours of the rainbow.”. Now, brown is obviously not exclusive to roots, but within roots, we only mentioned brown once. Within leaves, we presented all and independent options for colours too: green, yellow, red and brown. Etc.
For a more mathematical explanation, consider your tree to be a collection of elements. And a description is no more than naming different logic sub-sets in the finite collection of elements that represents the tree. Now, for all purposes of a logical or mathematical analysis, you make it easier if all sets are independent, and you definitely don’t want to leave any element behind. Therefore being M.E.C.E. is the equivalent of turning your Venn diagram into a nice puzzle and not missing any piece. Of course, for each puzzle piece, you can create an even smaller collection of elements, which you should also try to make M.E.C.E. within themselves. A puzzle within a puzzle.
MECEness is a big part of my day. I use it to create product taxonomies, to write better and cleaner emails, to point out problems and possible solutions, to structure excel’s model variables . A big part of my value as a founder and CEO is to be structured. And the biggest part of it is the M.E.C.E. effort.
1. Check my text about cohorts to find an orthogonal cohort model, which is quite M.E.C.E.!