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The Advantage Blog

  • Theodore O. Prosise Ph.D.


Updated: Jul 13, 2023

Steven Wright observed that “there is a fine line between fishing and standing on the shore like an idiot.” And as David St. Hubbins (lead singer of Spinal Tap, the band chronicled in Rob Reiner’s Rockumentary This is Spinal Tap) notes, “It’s such a fine line between stupid, and…uh…clever.” Well, there is also a fine line, based on my observations of jury deliberations, between reasonable inferences and conjecture/speculation. Jurors struggle mightily with these issues and seldom know where that fine line is or where it should be drawn.

As a former professor of communication specializing in persuasion and argument, observing and understanding juror behavior and then identifying practical solutions to the issues confronting trial teams is fascinating and creative work.

Conjecture/Speculation and Inference

Identifying when conjecture and speculation evolve into a reasonable inference can be very challenging. One person’s inference is another person’s conjecture, and vice versa. It is helpful to look at the definitions of these concepts to see why the line between the concepts is so thin.

Conjecture is defined as “an opinion or conclusion formed on the basis of incomplete information.” Similarly, speculation is defined as “ideas or guesses about something that is not known.” The focus of these definitions is on the use of incomplete information to reach a conclusion. But making a reasonable inference based on incomplete information is a fundamental characteristic of everyday decision-making.

Argument scholars Inch and Warnick instruct that, “When we reason, we make connections, distinctions, and predictions; we use what is known or familiar to us to reach a conclusion about that which is unknown or unfamiliar.” These scholars conclude that “practical argument” or informal logic lives in the realm of probabilities of conclusions, not certainties. We reason¬—make an inference¬—from what we know, see, and observe to draw a conclusion about something that is NOT certain or known, but is probably true, correct, or accurate.

Informal logic is distinct from formal logic in that it is reasoning based on probability. It is about deriving a conclusion that lies in the realm of probability, whereas formal logic (popularized by Sir Arthur Conan Doyle’s Sherlock Holmes) is based on the certainty of conclusions and elementary deductions. Just as we learn from mock jurors, so Sherlock Holmes is inspired, albeit in his extremely arrogant manner, from Watson’s pedestrian “logic”, in The Hound of the Baskervilles:

“I am afraid, my dear Watson, that most of your conclusions were erroneous. When I said that you stimulated me, I meant, to be frank, that in noting your fallacies, I was occasionally guided towards the truth. . . Now, you will observe that he could not have been on the staff of the hospital, since only a man well-established in London practice could hold such a position, and such a one would not drift toward the Country.”

The classical form of formal logic is the syllogism (e.g., All humans are mortal; Bob is a human; therefore, Bob is mortal). But practical argument is different from formal logic. Holmes follows a similar form with the absolutes of his statements: “He could not have been…since only a man…one would not drift…” But, again, the search for understanding of what probably happened or could have happened in our world is not directed by such certainties.

Recently, I observed a mock trial where a central question the jury was trying to decide was proximate cause. Beyond the general confusion jurors were having with the court’s proximate cause language, the jurors were trying to determine if the actions of the officers in allowing an individual to maintain possession of a deadly weapon was a proximate cause of death. The questions was, in essence, “If not this weapon, would the murder have occurred?” The jurors knew the weapon was the murder weapon. What the jurors were trying to figure out was whether another weapon could or would have been used if this one was not available.

During deliberations, not to mention in everyday life, some individuals devalue the use of informal reasoning which leads to probable conclusions, citing it as a reason to dismiss arguments made by one side or the other in a case. A recent mock trial illustrated this practice. Here are a few exchanges from that project.

In terms of the Defendants’ Conduct: Juror C: “Other people in a similar situation would have done it differently.” Juror B’s retort: “We don’t know that, that’s speculation.”

In terms of the Intentional Tort Feasor’s conduct: Juror D: “We know he would have done it, because he was motivated to do it.” Juror E’s Retort: “No, that’s speculation that he would have done it with something else” (Note: referring to the conclusion, which was an inference based on the presence of circumstantial evidence). Juror B: “He could have used something else…” Juror E: “Yeah, he could have, but this isn’t about what he could have done, it is about the facts.”

In terms of general issues in the case: Juror E: “You’re not supposed to assume, you go with the facts.” Juror E: “But you are just saying it is probable, not that it’s true.” Juror A: “I can’t say with certainty, but I feel this way.” Juror D: “How can we know that? You can’t assume.”

Typically, the use and misuse of the “speculation” dismissal is self-serving. Reasonable inferences become inappropriate speculation when they are made by the other side. However, dismissing the conclusion of another because it fails to provide certainty is a misunderstanding of the nature of practical logic. It is inappropriate to dismiss an argument as being “based on an assumption or speculation” when it is a reasonable inference based on facts and evidence. Drawing a conclusion about what is likely, based on observable data and facts, is a reasonable and appropriate practice.

Confronted with the challenges of practical reasoning and not knowing where and how to draw the line between speculation and reasonable inference, too often jurors retreat to phrases like “I feel…,” “I believe…,” and “I think…,” motivated by their overall leanings in the case. Well, what to do?

The Importance of Teaching Jurors How to Fish

The solution to the speculation/inference confusion partly lies in teaching jurors how to fish, not giving them a fish. That is to say, in closing argument, teach them how to reason with informal logic and how to judge when a proper inference has been made, as distinct from speculation or conjecture. Use an example or two to arm your jurors.

Warnick and Inch’s Critical Thinking and Communication summarized, drawing from Chaïm Perelman and L. Olbrechts-Tyteca’s The New Rhetoric: A Treatise on Argument, conjectures that there are six basic types of informal logic people use to make sense of situations and reasoning, based on available evidence, to what is more likely true than not. Although going into all six of these forms of reasoning is beyond the scope of this article, they are: 1) Quasi-logical reasoning; 2) Causal reasoning; 3) Generalization; 4) Co-existential or “sign” reasoning; 5) Analogy; and 6) Dissociation For jury trial, we have found sign reasoning to be one of the most used forms of informal reasoning in the deliberation process. Because it is used so often by jurors and can be easily misused, we suggest that you educate jurors to employ it effectively.

Use Sign Reasoning

We have applied many forms of informal logic in case strategies, but for illustration, I will focus on co-existential reasoning or “sign” reasoning. This form of reasoning is often used by jurors and under-utilized in closing arguments.

The use of sign reasoning is fairly simple and commonplace. People associate the presence of an unknown/unobserved fact (the conclusion), condition, or event in terms of the known/observable facts, events, or conclusions. For example, if people have wet hair and they are closing their umbrellas, it is a sign that it was raining.

There are three basic tests of sign reasoning.

Test One – The quantity of signs (observable facts). Test Two – The quality of the sign or signs (or the weight or importance of the observable signs). Test Three (a mirror image amalgam of the first two tests) – Are there many or particularly weighty signs (observable conditions) inconsistent with the presence of an unobservable condition?

Jurors, albeit more chaotically that the textbook teaches, often work through these tests in their deliberations. Helping them understand the relevance of these tests in distinguishing between a reasonable inference and conjecture will arm jurors to stand up for their conclusions and ward off accusations of “speculation” when they are actually “reasoning.”

We have often structured major sections of the case story/case theme strategy and the closing argument around sign reasoning. One of the simplest, but most effective, uses is the “footprints in the sand” graphic with its accompanying rhetorical effort to show and convince jurors how the evidence leads to and points to the most likely conclusion.

In the mock trial noted above, the evidence included that the person had access to other weapons and witnesses testified that he had other firearms besides the one returned to him by law enforcement. The evidence also showed that the person could have obtained another weapon. In sum, the known or observable evidence pointed to the likely conclusion that if the subject did not use the returned weapon, he would have used another to commit his heinous act. The footprints (observable evidence) in the sand led to the conclusion that the crime would have happened whether a single firearm was returned to the perpetrator or not. There were no footprints leading toward the conclusion that it was this—and only this—firearm that was a cause of the murder.

Utilize the Jury Instructions Explicitly

Although the jury instructions direct jurors to weigh circumstantial evidence at least as much as direct evidence, there is a pejorative connotation to the phrase “circumstantial evidence” in common parlance. For example, “that’s just circumstantial” is a way to dismiss the evidence, almost like saying “that is coincidental.” Anchor your teaching on how to deliberate by displaying the court’s instruction on the nature of direct and circumstantial evidence. Help jurors understand by telling them directly that their job is to understand what likely happened when they were not there, did not see it themselves, and when there are different arguments being advanced about what really occurred. Orient them to the task before them; teach them how to fish by first helping them understand the process of making inferences—reasoning from the observed to concluding about the unobserved. Show the reasoning process visually, through an example, and teach them how to reason through the process.

I have noted many times before the importance of providing jurors with process graphics: visual reasoning roadmaps to help structure their deliberations. Jurors are looking for a way to proceed in deliberations and often are at a loss about how to establish the deliberative norms to guide their collective reasoning efforts. Map it out for them; give them the basic form of the process so they can use it and apply it generally.

Advocates need to arm jurors to control deliberations and push for a sound reasoning process. It is about how the evidence and facts point to a reasonable and sound conclusion. This strategy of controlling and directing the inferential process of juror deliberations is most useful in many trial situations. It doesn’t matter if the case is about employment discrimination, trade secret misappropriation, medical or legal malpractice, tort claims, or myriad other trial matters. If the case involves trying to understand what occurred based on what is available and observable, the reasoning process and the technique above fits the bill.


The fine line between conjecture and speculation on the one hand, and logical, practical, and sound inference on the other hand is, simply put, what you as the advocate make it. As advocates in trial, you have an incredible opportunity to organize, structure, and map the reasoning process that jurors should use in their evaluation of your client’s case. Too often, too much is left to chance. Trial teams are often surprised at verdicts and struggle to understand what the jury did. But, as this article notes, perhaps the better question to ask is how the jury verdict happened (or should happen). It is understanding how they “reasoned” that is the key to understanding the verdict. It is also the key to securing your next positive.


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