In litigation, presenting argument maps with implicit premises (i.e., enthymemes) is often appropriate. But it can be risky. Without the scaffolding that comes from depiciting all the premises, arguments may appear to the judge to lack sufficient rigor and precision. Or they may just appear to be confusing with the nature of the inference unclear.

A portion of an argument map from an Austhink Consulting report titled “Why Tanks? Why Abrams?” helps illustrate this risk. (I highly recommend reading this report. It is the most effective, dynamic, and innovative use of argument mapping for a large scale project that I have ever seen. I will enjoy and benefit from studying it for years to come. It is one of the best “arguments” for the power of argument mapping.)

The following map is the top tier of a large comprehensive map from the report which presents its final conclusion and most general reason. Based on the explanation of the visual grammar of this map, claims 1A-a and 1A-b are intended to represent two co-premises that comprise a single reason. But a quick examination of them reveals, in my opinion, that this is not so. The two co-premises are actually portions of two separate reasons. This is obvious because the Rabbit and Holding Hands rules are not followed. There are missing premises.

Based on claim 1A-a, the other co-premise need only state that “buying the Abrams tanks was buying new tanks” to complete a single reason. In fact, buying any of the competing tanks (i.e., Leopard 2 and Challenger 2) could also be valid co-premises resulting in their purchases as “sound decisions” as shown below.

This example illustrates the confusion that can result from not making explicit all the co-premises. The narrative in the report confirms that there are two separate reasons. It concluded that “[t]he decision to buy new Abrams A1M1 AIM tanks…was sound. p. 5. It was sound because buying new tanks was a sound decision (to maintain tank capability.) And “in maintaining that capability,” buying the Abrams tanks was sound because they were a better buy for the Army than any other available tank would have been. p. 5.

So one approach would be to consider these two claims as part of two separate reasons as shown below. (An essential predication transitivity map is also depicted.)

But an examination of the narrative suggests a different argument map. The first claim (i.e., A1-a) provides no diagnosticity to distinguish between the three available tanks. Buying any of them would have been a “sound decision. So either there are two final conclusion: “Buying Abrams was a sound decision. And buying Abrams was the soundest decision.” Or more likely, there is just one final conclusion: ”Buying Abrams was the soundest decision.” And a supporting (non-inferential) assumption is that “the purchase of new tanks (in general) was a sound decision.” This argument structure is shown below.

These examples illustrate why using essential predication transitivity always avoids this potential lack of clarity that can result from using other argument structures. There are never implicit inferential premises with an essential predication transitivity approach. (There may be differing degrees of granularity.) And the linkage between the co-premises is always obvious. In litigation, such precision and clarity is essential.