One of the strangest arguments I have heard raised in argument against the logical approach is that it means the expert will impinge upon the authority of the Court. I have heard this a few times recently. It is particularly troubling that this has come from lawyers. Unfortunately, this has always happened in a venue where I could not actually discuss the matter with them.

As an objection to the logical approach, this is the strangest argument I have ever heard, without a doubt. In fact, proper application of the logical approach is one of the few ways to ensure that this will not happen.

To clarify, it is important to first understand the concept of “usurping the role of the Court” which means, in essence, to improperly influence the court’s procedures and decision-making, often by speaking inappropriately to or about the ultimate issue. To be sure, there is a legitimate concern that this might happen, particularly with an expert. At the same time, it is certainly not a new idea and it has been written about literally for years.

It can be found in most codes and directives regarding expert evidence. Indeed, Justice Sopinka noted this issue in the 1994 R. v. Mohan ruling when he stated, in part, “There is also a concern inherent in the application of this criterion that experts not be permitted to usurp the functions of the trier of fact.” 

In part, this is a legitimate concern because an ‘expert’ is often seen as being all-knowledgeable and infallible (even when both such things are impossibility). People may view the expert’s opinion as being deserving of special consideration. In a limited way that is true, if only because expert witnesses are allowed to express their opinion about things, unlike other witnesses. But it is wrong to think experts are perfect and infallible. That is simply not true. 

Based on this mistaken belief it is possible that an examiner’s opinion could 1) be given too much weight, 2) replace or over-ride the opinion of the trier/jury, 3) be misused in a manner that distorts the fact-finding process, and/or 4) be confusing to the trier/jury. To be sure, this has always been the case and it is a particular concern when speaking about the approach traditionally taken by examiners in doing their evaluations and reporting. In part, this happens because experts have traditionally expressed opinions about ‘what happened’. That is, their opinion spoke to the probability of the events that may have happened to cause the evidence.

In that approach, such concerns are clearly legitimate.  

But, in contrast to that tradition, the logical approach takes a very different tack and, as a result, has precisely the opposite effect. Proper application of the approach goes a long way help ensure the examiner avoids doing what the lawyers think they would be doing by using it. It is a conundrum to me that lawyers, who are trained in matters of both law and logic, think this way. It is very problematic and speaks volumes about the state of knowledge and awareness with respect to the logical approach and how it actually works. 

Reality is exactly the opposite of what they think it is.  

I find it especially hard to understand in light of the vast literature that has been written about the logical approach in the last couple of decades.1 However, in fairness, people (including myself many years ago) sometimes find it difficult to see and understand the distinction between the way things have traditionally been done and the way that proper logic dictates things be done.

For one thing, nobody wants to believe that their way of doing things is logically fallible or unwarranted. For another, people (e.g., lawyers and some judges) want the expert to speak directly to the issue at hand. In general, it makes sense that they should be able to do that. After all, they are an expert and people express things in that manner all the time in their daily lives. The problem is that the knowledge and information the expert possesses is insufficient for that purpose. 

The important thing to understand is that, even though examiners do not possess the requisite information to express such opinions, they can definitely assist another party in their efforts toward that goal.  

I suspect that some of the confusion may come from mistakenly equating the logical approach and Bayes Theorem. The two are NOT the same as I’ve discussed at length elsewhere. Bayes Theorem is a logically coherent process for belief updating and, as such, it might be a good way to conduct something like a trial. A trial, after all, is the ultimate belief updating process.2 The key, however, is that the belief being updated is not that of the expert; it is that of the trier. To that end, the expert’s role within the logical approach is very limited and constrained. The expert (simply) assists the trier (judge and/or jury) in their determinations by explaining what domain-specific evidence means in a specified context. They do this by speaking solely to the evidence and never the propositions.

As a result, there is absolutely NO way this process can usurp the authority of the court because no opinion is ever given in terms of the probability of the propositions of interest. 

Another issue might be the setting of propositions as a concern for those lawyers. The setting of propositions is a legitimate concern but, as discussed elsewhere, that isn’t something the expert should, or would, do if it were not the only viable option in some cases. Perhaps it is the idea that the logical approach ‘requires’ two competing propositions to conduct a proper evaluation. Some lawyers like to point out that, in many legal systems, the defense need not hold or present a ‘position’ at all. These ideas miss a couple of key things: first, there is always a counter-position that can be considered (the negation, if nothing else, even if that’s not the ‘best’ option for the defense); second, all traditional evaluations incorporate a counter-position even though it usually remains hidden or masked. I am, by no means, the first to point these things out.

A set of competing propositions is key to proper evaluation of evidence so they must be set or declared. If this is done by the examiner, then the set used must be declared so everyone knows what was done (and provide alternatives, if something else is preferred).

Complicating matters is the fact that people (including lawyers) tend to ‘automatically’ transpose the conditional. People do this in their regular lives all the time. We observe and evaluate constantly and we then make a ‘decision’ based on those things with no conscious effort. As a rule, such a process works quite well for routine ‘decisions’ made by people in their daily lives. But it can result in unexpected and fallacious outcomes as well. 

It is important to understand that forensic experts have historically been trained to do this in their work. They are literally taught that certain observations mean that something ‘must’ have happened. While that may be true in some rare situations, it is not generally a sound approach because it ignores uncertainty about the relationship between evidence and cause. 

Additionally, lawyers also do this all the time. For them, this is not a problem because 1) it is part of their role, and 2) they have more complete knowledge of the situation. As such, they are in a position to consolidate all of the relevant information when formulating their belief. They can also apply whatever personal criteria they like to form their opinion so that they can then present that belief to the court as the argument for their side of the matter. 

Similarly, judges do this to reach their final opinion in a matter. In essence, the trier must listen to, and assess, the information provided by various sources (i.e., witnesses) and then determine ‘what happened’ as a cause of the overall evidence. They will, of course, listen to the lawyers who frame that information in the best possible way (for their side). Ultimately, they must consolidate all of the relevant information and apply some decision criteria or heuristic. Again, this is not a problem because 1) it is their role, and 2) they have access to all the necessary information, even moreso than any lawyer.  

Experts are NOT in the same position. They provide fairly limited and discrete information about one aspect of the matter. That information relates, and is limited, to issues within the scope of their expertise. As such, transposition that leads to a statement about the proposition(s) is never warranted or justified. If an expert adheres to the principles and processes embodied in the logical approach, they will never express an opinion that can possibly be viewed as usurping the authority of the court. They will, in fact, never make a statement about the truth/falsity/probability/likelihood of any proposition.

Why? Because their opinion is limited to a statement, or statements, about the evidence in terms of each of the relevant propositions if each of those were actually true. The evidence, therefore, provides support for one or the other (or both, to varying degree) of the competing propositions. 

Another complication is the lack of standardized wording for opinions. The choice of the opinion wording is subject to discussion/debate but I prefer those in the form of a concordance scale recommended by ENFSI. That scale ties the verbal opinion to a clear level of relative belief about the propositions. It is prescriptive in nature, not descriptive. Admittedly, there is an open question as to whether or not a given method or examiner can use such a scale reliably and accurately. However, that point, while important, is not an argument against using the logical approach. After all, there is little standardization for opinion scales used with the traditional approach.

Most critics of the logical approach never bother to think about the alternative that would be used if the logical approach is not applied. A few judicial rulings critical of the logical approach have been flawed in this manner, even though the Court in those rulings attempted to be logical and sensible in their critique.  

If one does not follow the logical approach: 

  • the opinion will be in the form of a transposed statement about the propositions, 
  • the opinion will not be logically sound or coherent, 
  • there will be no way for the trier to properly dis-entangle the expert evidence to apply it in their own reasoning, and 
  • there would be a legitimate concern that the expert’s opinion could usurp that of the Court to some degree.  

As it turns out, all of those things are found in the traditional methods and wording used by examiners for decades. It is only through the adoption, and proper application, of the logical approach that these issues can be avoided.

Now, lawyers tend to be good at reasoning, but in this particular argument they demonstrate a complete and utter misunderstanding of the logical approach, how it works, and what information it provides. They understand what is required of the expert, yet fail to appreciate two critical things:

  • the traditional approach fails to achieve what is required by the court, and
  • the logical approach is the only way to actually achieve that objective.  

Sadly, little will change until this becomes the common understanding amongst the various parties involved in our Justice system. I fear that is a long way off.  

  1. Of course, these concepts are neither new or recent. The logical approach has been known (and used by some examiners) since the late 1800’s.
  2. Please understand I am not saying this is how a court should function. It makes a lot of sense but, in the end, how things are done is entirely up to the judge.

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