New Zealand Law Society - Facts, truth and inferences

Facts, truth and inferences

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In this column I have previously spoken of the litigator as a story teller. I have also written on the influence of truth on the creation of narratives. Here, I would like to discuss the tools with which instructive and persuasive stories are built – whether they be in fact, in law or in both fact and law.

The most persuasive advocates are not necessarily those with the highest IQ. They are also not those who can necessarily construct the most complex of legal arguments. The most persuasive of advocates are, I believe, counsel who understand human nature, who understand how to construct a narrative and to deliver it with the skill of a story teller, drawing the listener in to their world, manufactured according to basic principles of logic and reason.

Many of the great advocates have developed their skills through experience and the development of judgement. But one need not entirely rely upon experience and the development of judgement to be a proficient advocate – they are skills that can be taught.

Good, clear, convincing argumentation and the ability to successfully deconstruct and critique the arguments of others can and should be taught to our undergraduate law students for this to be followed through into continuing professional education.


Let us take one aspect of good argumentation – inferences. Great advocates know how far they can push inferences from the evidence at hand.

Such an exercise is laced with pitfalls. Too often case theories outstrip the facts upon which they are supposedly based. Factual assertions often stretch beyond that which is necessary. Unnecessary elements appear in theories often in an effort by advocates to present a complete story with little awareness that a failure to establish such superfluous elements undermines those necessary and good elements of a case theory.

Conversely, in some cases gaps are created or left unplugged in ignorance of their significance to the establishment of the legal case whether that be for the prosecution, defence, plaintiff or respondent.

Circumstantial evidence is the bedrock of inferential reasoning.

As advocates, we are well aware that a case is not “weak” by virtue of it being based upon circumstantial evidence alone (a common misconception). Circumstantial evidence will often form the base of a strong case, again, in both the criminal and civil jurisdiction alike. But the inferences drawn from prospectant, concomitant, and retrospective circumstantial evidence is all too often tenuous – and seemingly unwittingly so.

Seeing the frequent stretch of conclusions from circumstantial evidence, I am drawn to the conclusion that the generalisation or premise upon which such inferences are co-founded must have remain unsaid, unacknowledged and therefore unscrutinised when formulated in the mind of the advocate.

What do I mean by this? Arguments ought to follow the basic rules of logic. An established premise stands side by side with an established premise[s] from which a cogent argument can be drawn if the principle of valid reasoning is followed.


Failure to identify a generalisation upon which a conclusion is drawn is tantamount to withdrawing a key premise and therefore threatens the cogency of the conclusion by undermining the validity of the reasoning.

Failure to identify the generalisation does not mean, of course, that it does not exist. However, without expressly identifying the generalisation the argument runs an unnecessary risk of opposition scrutiny; scrutiny that would likely be avoided or minimised if the generalisation had been “named-and-shamed” as I like to put it.

Let me give an example. In attempting to establish the factual assertion that Rover is a dog, we might identify the fact that Rover barks. If we attempt to draw our conclusion from this alone the argument is incomplete – it is a non sequitur.

Of course we would not attempt to draw such an inference on the one piece of evidence – that Rover barks. What we must do is expressly identify the remaining premise[s] upon which we seek to rely – namely our generalisation that all dogs bark. All generalisations in such cases need to be blatantly obvious. If they are not then it is likely we open ourselves to challenge and at worst open ourselves to the possibility that the fact finder will not agree with our inference and therefore reject our factual proposition.

Of course, in our Rover example our argument remains a non sequitur even with our second premise – it suffers from invalid reasoning. This could be fixed in one of two ways. Either the modification of our inference “Rover is a dog” to “it is likely that Rover is a dog”. However, even this inference should be accompanied by a further premise, ie “that 95% of all barking animals are dogs” for example.

The second way in which we can correct the reasoning of our first inference – the categorical conclusion that Rover is a dog – is by adding a premise that “all barking animals are dogs”. A glib approach to mapping this seemingly simply argument could have resulted in a line of invalid reasoning or at the very least very weak reasoning.

Exposing premises

There is great benefit to clearly exposing all premises relied upon (whether they be items of real evidence or mere presumptions, biases, generalisations or even prejudices).

The first is that we are much better placed to clearly identify any weakness in our arguments before such a state of affairs is identified by others. All generalisations ought to be clear, simple and unassailable. If they are not then they are not likely to be agreed with by your audience and will therefore require further proof to establish.

Of course in law probabilities are our bread and butter – we seldom deal in absolute, incontrovertible truths the provenance and significance of which cannot be questioned. Failing to identify all presumptions that influence our decision-making (our process of drawing conclusions) will often result in accusations of invalid reasoning leading to the destruction of what may have otherwise seemed a cogent or sound argument.

While story telling may seem the product of alchemy, the construction and presentation of valid and cogent arguments is not reserved to only those with 30 years’ experience. It can be learnt and mastered for the benefit of your clients and the system as a whole.

Dr Chris Gallavin is an Associate Professor and Dean of Law at Canterbury University. He has published extensively on criminal justice and on evidence and procedure in particular. He is the author of the appellant handbook, Evidence(LexisNexis, Wellington, 2008), and regularly undertakes consultant work in the area of the law of evidence.

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