Language Modeling for Legal Proof
Le Cheng
Winnie Cheng
Research Centre for Professional Communication The Hong Kong Polytechnic University Hong Kong, China
[email protected]
Research Centre for Professional Communication The Hong Kong Polytechnic University Hong Kong, China
[email protected]
Abstract— In common law jurisdictions, the notion of proof beyond a reasonable doubt is frequently related to notions such as the belief or certainty of a judge or a juror about reality. The notion of balance of probabilities is however related to likelihood or probability. In this analysis, we link belief and proof by introducing the notion of epistemic modality, which is concerned with speaker’s belief in propositional probability. The variation in the orientation of epistemic modality helps to integrate the two levels of proof and bridge the apparent test gap between them. The analysis further introduces the notion of relevance in order to clarify the nature of legal proof by taking rape cases as example. This analysis then provides an integrated language model to improve but diversify the expressions in terms of burden of proof.
II.
A. Certainty in Law “In this world nothing can be said to be certain, except death and taxes.”[1] Philosophers and jurists have already come to realize that in human world, as opposed mathematical or logic field, no absolute certainty can be had. Therefore, the law does not require the prosecution to prove its case with absolute certainty. In other words, it is, widely accepted that absolute certainty is unattainable and would entail excessive rigidity. Hence it is recognised that a prescription by law inevitably may involve some degree of vagueness in the prescription which may require clarification by the courts, whether in substantive law or in the law of procedure. Then the next best is that the court “must govern itself by a moral certainty” or a “virtual certainty” (See Lydall v. Weston (1739) 2 Atk. 19, R v. Moloney [1985] AC 905, Victor v. Nebraksa (92-8894), 511 U.S. 1 (1994), and HKSAR v. Mach Sindy [2004] CACC 198), for it is almost impossible in the nature that there should be a mathematical certainty in law. This sort of certainty “moral” not because it had anything to do with ethics and morality but to contrast it with the “mathematical” certainty traditionally associated with a rigorous demonstration. Moral certainty is another way of saying beyond a reasonable doubt. For criminal cases, it is necessary to prove each and every essential integrant, unless otherwise provided. In a criminal trial, the reasonable belief (but falling short of absolute certainty) of the trier of the fact (jury or judge sitting without a jury) that the evidence shows the defendant is guilty. In civil cases, the standard of proof is balance of probabilities, which means more probable than not.
Keywords- legal proof; language modeling; probability; belief; modality; relevance
I.
EPISTEMIC MODALITY AND BURDEN OF PROOF
INTRODUCTION
In common law jurisdictions, including Hong Kong, the notion of proof beyond a reasonable doubt is frequently related to notions such as the belief or certainty of a judge or a juror about reality but he notion of balance of probabilities is however related to likelihood or probability of a proposition. The two levels of burden of proof can find various expressions in court. Just because of such diversities in the expressions testing the burden of proof and different approaches to burden of proof, the association of proof with fact finder‟s belief is often criticized. However, there is a controversy in law, that is, the witnesses who know the reality or truth cannot decide on facts, but it is judges or jurors who are distant from the reality that find facts. It is therefore natural that the fact finders are seldom actually certain about proof which is the basis of factual reconstruction, in other words, they can only moral certain, if it is, about proof. Belief inevitably, though controversially, becomes a core notion in burden of proof. In this analysis, we link belief and proof by introducing the notion of epistemic modality, which is concerned with speaker‟s belief in propositional probability. The variation in the orientation of epistemic modality helps to integrate the two levels of proof, that is, proof on balance of probabilities and proof beyond reasonable doubt. The analysis further introduces the notion of relevance in order to clarify the nature of legal proof by taking rape cases as example.
B. Types of Burden of Proof Now that there is no absolute certainty in law, two techniques, that is, presumptions and burden of proof are used to reduce the difficulty of corroboration. Presumptions can obviate the need for proof, or make the process easier; on occasions they are irrebuttable. The standard of proof is the level of proof required in a legal action to convince the court that a given proposition is true. The degree of proof required depends on the circumstances of the proposition. Typically, most common law countries have two levels of proof: proof on the balance of probabilities at the low level and proof beyond a reasonable doubt at the high level. In the US and Mexico, there exists, though controversially, a third standard 1
called clear and convincing evidence which is the medium level of proof. Probable cause is usually used in the US as a standard to issue a search warrant or grant prejudgment remedy. In Hong Kong, as well as in other common law jurisdictions, proof on a balance of probabilities is used in some categories in criminal proceedings such as the special defence, the evidential burden, and the persuasive burden, where an onus is placed on an accused. Although many efforts have been devoted to the quantification of probabilities, it seems clear that there is no consistent conclusion about the percentage of beyond a reasonable doubt or other standards of proof, if there are, except that it is commonly accepted that balance of probabilities means higher than 0.5, as Lord Nicholls in Re H (Minors) [1996] AC 563 at pp.586-587 of Birkenhead pointed out that a preponderance of probabilities is a probability of >0.5 on a scale from 0 (impossibility) to 1 (certainty). Therefore, quantification is not the focus of this study. Since there is no exact measure of certainty it is always somewhat subjective and based on reasonable opinions of judge and/or jury. However, it is still worthwhile to give a typological framework of standard of proof modeling after logic and mathematics. Although the standards are quite stationary, but the formulas to test such standards vary. Such a phenomenon can be well explicated by Lord Morris (Hornal v. Neuberger Products Limited [1956] 1 QB 247, cited in A Solicitor v. The law society of Hong Kong [2005] CACV 107) as follows: It is, I think, clear from the authorities that a difference of approach in civil cases has been recognized. Many judicial utterances show this. The phrase „balance of probabilities‟ is often employed as a convenient phrase to express the basis upon which civil issues are decided. It may well be that no clear-cut logical reconciliation can be formulated in regard to the authorities on these topics. But perhaps they illustrate that „the life of the law is not logic but experience‟. Lord Denning in Miller v. Minister of Pensions [1947] gave a celebrated definition for proof beyond a reasonable doubt from the angle of probabilities and possibilities: Proof beyond reasonable doubt does not mean proof beyond a shadow of a doubt. The law would fail to protect the community if it admitted to fanciful possibilities to deflect the course of justice. If the evidence is so strong against a man as to leave one a remote possibility in his favour which can be dismissed with the sentence, „of course it is possible, but not in the least probable,‟ the case is proved beyond reasonable doubt but nothing short of that will suffice. (Emphasis added) Such an understanding is of course widely endorsed in Hong Kong. Besides, we can see other tests such as “sure”, “firmly convinced”, “moral certainty” or “virtual certain” as follows: Each accused is presumed innocent unless and until proven beyond reasonable doubt to be guilty. So the thought that he may have been more interested in
getting himself acquitted than in telling the truth should not form any part of your thinking when deciding whether to acquit or convict him. It is, however, something which you may take into account when deciding whether you feel sure that what he says against a co-accused is true. All of this, too, is simply a part of the law that if there is any reasonable doubt as to an accused‟s guilt, then he must be acquitted.” Law Chung Ki & Another v. HKSAR FACC6/2005. Reported in: [2005] 4 HKLRD 499; (2005) 8 HKCFAR 701 (Emphasis added) TABLE I.
Application Not as a standard of proof in common law; as one and the only one in some civil law jurisdictions; not directly In common law jurisdictions (e.g. HK) as a standard of proof in criminal proceedings In most common law jurisdictions, including HK as a standard of proof in civil proceedings In the US as a standard for search warrant or prejudgment remedy Not directly Not directly
TYPOLOGICAL FRAMEWORK OF CERTAINTY
Level certainty Absolute certainty
of
Beyond reasonable doubt
a
Expression necessity/necessary/necessarily Certain/(full) certainty/certainly Beyond all/any (possible) doubt Mathematical/logical /scientific certainty True/truth; real/reality Virtual/moral certainty Virtually/morally certain (firmly) convinced (absolutely/entirely) sure
Balance of probabilities/ Preponderance of probabilities/ Preponderance of evidence
More likely than not (true) More Probable than not
Probable Cause
Probable; likely; reasonably possible; a real/reasonable possibility
Remote possibility Impossibility
Remote possibility (absolutely/entirely) impossible; impossibility
Proof by clear and convincing evidence, which is often tested as substantially more likely than not, is required where particularly important individual interests or rights are at 2
stake. See, e.g., Santosky v. Kramer, 455 U. S. 745 (1982) (proceeding to terminate parental rights); Addington v. Texas, ibid, (involuntary commitment proceeding); Woody v. INS, 385 U. S. 276, 285-286 (1966) (deportation). In Miller v Minister of Pensions [1947], Lord Denning described the
proposition and modality). In the median value, the negative is freely transferable between the proposition and with the outer values (low and high); if the negative is transferred the value switches (either from high to low, or from low to high) [7] Based on the analysis above, an overall framework of epistemic modality can be proposed as indicated in TABLE II. If we compare TABLE I and TABLE II, it is not difficult to establish a correspondence between near necessity in epistemic modality with the formulas for proof beyond a reasonable doubt.
balance of probabilities, also known as preponderance of evidence or preponderance of probabilities, simply as “more
probable than not”; the same standard, was defined as “more likely than not” in Re H and R [1996] AC 563; [1996] 1 FLR 80. In Hong Kong, the expressions clear and convincing, absolutely certain, and probable cause can be found, not explicitly as a standard of proof in court proceedings. The courts in Hong Kong basically follow the practices in the United Kingdom, that is, to apply proof on the balance of probabilities in civil proceedings and proof beyond a reasonable doubt in criminal proceedings, although the degree of proof may vary according to the nature and gravity of a case. Based on some court judgments which cover burden of proof in Hong Kong available at http://www.judiciary.gov.hk/, a rough typological framework can be worked out as in TABLE I.
TABLE II.
AN OVERALL FRAMEWORK OF EPISTEMIC MODALITY
Orientation
Expressions and Value of Probability median [M]
outer low[L]
[will (be), probably, not probable that]
C. Burden of Proof, Belief and Modality Scholarships over past years have related judicial declarations of proven facts to the belief of judges or jurors. It is also common to find references to belief in relation to proof in legislation and in jurisprudence. As [2] has keenly noticed, most suits, then, are “facts suits”—suits in which the decisions depend solely on the beliefs of the trial judges or juries about the past events the occurrence of which is in dispute. Balance of probabilities, used in civil cases and also in some categories of factual identification in criminal proceedings, is often explained by some objective expressions such as more likely than not (true) or more possible than not (true), and proof beyond a reasonable doubt is frequently related to subjective ones such as sure, firm belief or firmly convinced. Modality is essentially “a matter of degree” [3]. Epistemic modality, by indicating the speaker‟s belief or confidence in most cases, is concerned the speaker‟s assumptions or assessment of possibilities [4]. There are variants of the expression of modality. In explicit expressions, the speaker construes the proposition as a projection and encodes the subjectivity (I think), or the objectivity (it is likely), in a projecting clause. For those leaving implicit the source of the conviction, they also differ along the subjective in the verb form such as must or objective dimension in the adverbial form such as certainly [5]. In Epistemic modality, “there may be seen in terms of three types of conclusion, a possible conclusion with may, the only possible conclusion with must and a reasonable conclusion with will” [6]. Therefore, the value that can be attached to epistemic modality is high, median or low. In a linguistic perspective, epistemic modality can be negated. Negative forms include Straight Negative (SN: negative on the proposition), Transferred Negative (TN: negative on modality), and Double Negative (DN: negative on the
Implicit & subjective
will
Implicit & objective Explicit & subjective Explicit & objective
probably
[may/can (be), possibly, not certain that] may, might, could possibly
I think that it is supposed that probably (…) not
I doubt that it is possible that possibly (…) not
TN
not probably
DN
not probable that....not
not possibly [H] not possible that…not [H]
SN
high[H] near necessity necessity [almost/nearly [must (be), certain] necessarily, not possible that]
must
almost necessarily I am sure/ almost certain It is almost certain that almost necessarily (…) not barely certain (L) almost necessarily that… not (L)
necessarily I am certain that it is necessary that necessarily (…) not not necessarily [L] not necessary that…not [L]
If we accept that epistemic modality indicates fact finder‟s belief, regardless of its orientation, we can say any expression with high value, whether near necessity or necessity, can be an expression to conclude that a proposition is beyond a reasonable doubt. As to the median level, the expression “more likely than not (true)” or “more probable than not (true)”, as well as its adverbial equivalent “more probably than not”, can denote the concept of balance of probabilities. Although law is not different from logic, but logic still has, as it has had, its application in law. So, if we say it is impossible that p, which can be transferred as it is necessary that not p; similarly, it is a bare/remote possibility that p can be transferred as it is almost certain that not p. Those expressions can therefore also be taken as formulas to establish proof beyond reasonable doubt. It is also true that it is less likely that p can be transferred as it is more likely than not p, then as a sufficient test for balance of probabilities. 3
The law looks for probability, not certainty. But probability is an unsatisfactorily vague criterion because there are degrees of probability. In establishing principles regarding the standard of proof, the law on one hand seeks to define the degree of probability appropriate for different types of proceedings, proof on balance of probabilities in civil proceedings and proof beyond a reasonable doubt in criminal proceedings; on the other hand, in order to distinguish between the different levels, different orientations is adopted, that is, the former usually with objective expressions and the latter often with subjective ones. In dealing with the question of what constitutes proof beyond reasonable doubt, courts try their best to eschew all reference to the terms “probable” and “probability” whenever it is necessary to refer to the two standards of proof lest the jury tend to confuse the two standards. The apparent deviation of proof beyond a reasonable doubt from probability seems violate the core task of courts---to establish probabilities in law.
(b) at that time he knows that she does not consent to the intercourse or he is reckless as to whether she consents to it. In order to convict defendant of this charge, the Prosecution must prove (make jury satisfied) the following elements beyond a reasonable doubt: (a) the defendant (a man) committed an act of sexual intercourse with the victim (a female); (b) the victim did not consent to it at the time of the intercourse and (c) the defendant acted intentionally, knowingly or recklessly. The former two are actus reus, and the latter is mens rea. If the defendant raises a reasonable doubt against the Prosecution‟s evidence, then the benefit of doubt will stay with the defendant. B. Defences to Criminal Liability Criminal liability presupposes that the person who is being held liable is responsible for his or her action. Some defences, such as incapacitating conditions, justification or excuses, can challenge this assumption on balance of probabilities. A person who has done a criminal act may not guilty of an offence, if the defendant does not (or did not) possess the necessary mental capacity to be held “criminally” liable [12]. Those factors include: ·Age--- A child under 7 is irrebuttably presumed to be incapable of committing any offence. A child of or over 7 but under 14 is criminally liable for any criminal act done with mischievous discretion, but a boy under is irrebuttably presumed to be sexually incapable (CL 2.2.1, 2.2.2, 2.2.3). ·Insanity--- Insanity caused by a disease of mind at the time of committing the offence also negates mens rea (CL 2.3.2) but the burden of proving insanity rests on the party who makes a request. · Automatism--- Automatism (CL 2.4) includes all unconscious acts, the result of external causes beyond the mental control of the defendant as distinct from those caused by the disease of the mind (internal causes). A person is however criminally liable whose automatism is self-induced (CL 2.4.3). A person charged with an offence will be acquitted if he/she successfully raises any one of the following justification and excuses such as mistaken (CL 2.9) and conduct of the victim (CL 2.10). In rape cases, the victim’s consent or the mistaken but genuine belief in the victim’s consent can be a justifiable defence to criminal liability.
The building of standards of proof into epistemic modality, on the one hand, helps to account for different expressions in proof, whether in the form of probabilities/possibility, or in the form of sure, certainty, or necessity, under the same umbrella, that is, the belief of judges or jurors as fact finders, and on the other hand such an explanation bridges the gap between legal discourses and non-legal discourses. III.
LEGAL PROOF AND RELEVANCE
When a piece of evidence is introduced before the court, only when it satisfies the corresponding standard of proof can it be admitted as proof in law. But not all information is evidence or proof unless it is relevant to the objects to be proven. These objects are some abstract (sub)categories, for example in criminal law, which are essential ingredients of offence, factors as defence, or factors mitigating, enhancing or aggravating sentencing. This part will take rape cases in Hong Kong as an example to illustrate how relevance is related to legal proof. By using the Digest of Hong Kong Criminal Law (which is based on Criminal Ordinances and cases, hereafter as CL) [8], the Digest of Hong Kong Criminal Procedure [9], the Bilingual Laws Information System [10] and the court judgments and the cases cited therein at the Legal Reference System of Hong Kong [11], we can identify the elements and factors for rape as follows.
C. Factors Affecting Sentencing Besides these defences negating or affecting the criminal liability, there are other factors affecting the sentencing. A court should not sentence a defendant to imprisonment unless legislation makes imprisonment mandatory. A court may sentence a person under the age of 21 years to imprisonment only if satisfied that on other form of sentence is appropriate [13]. For organized and serious crimes (OSC) such as rape, there are enhanced sentences if the prosecution presents information concerning the follow matters [14]: (a) the nature and extent of any harm caused, directly or indirectly, to any person by the act in respect of which the
A. Elements of an Offence and Criminal Liability Two elements, or indispensable factors, are required to establish criminal liability: actus reus and mens rea. Actus reus and mens rea must coexist for most offences. Criminal liability is established only if the actus reus is done by the defendant under the control of the defendant‟s mens rea (CL 1.2.1). If either element is absent, or if the two elements do not coexist, criminal liability does not arise. According to Section Criminal Ordinance of Hong Kong, a man commits rape if- (a) he has unlawful sexual intercourse with a woman who at the time of the intercourse does not consent to it; and 4
person has been so convicted; (b) the nature and extent of any benefit, whether financial or otherwise, that accrued or was intended to accrue, directly or indirectly, to that or any other person from that act; (c) the prevalence of that specified offence; (d) the nature and extent of any harm, whether direct or indirect, caused to the community by recent occurrences of that specified offence; (e) the nature and extent of the total benefit, whether financial or otherwise, accruing directly or indirectly to any person from recent occurrences of that specified offence. It is the settled practice that a full 1/3 discount should be given if a defendant pleads guilty [15]; as to other mitigating factors, 1/10 discount is assign for each [16]; for the offences related to the Organized and Serious Crimes (OSC), enhancing the sentence by 1/3 would be appropriate. For other aggravating factors, 1/5 is added for each [17]. This formula provides a guideline, but the real cases are more complicated. During the course of trial, the defendant and the Prosecution can file all the proofs in bundle, but in the instructions to the jury, those related to sentencing are not allowed to be introduced to jury before its deliberation of verdict on the defendant‟s (not) guilt. Mitigating factors include a guilty plea, reparation to a victim, personal hardship, good character, remorse, or good conduct since the commission of the offence as evidence of reform, youth, disability, psychological problems, and addiction to drugs. Besides, the variants of offence, preparatory or inchoate offences, will also influence the sentencing. IV.
rape cases, limits the court adjudication to narrow discretion and therefore helps the maximum realization of fairness and consistency. It is, however, difficult to assign an exact value to a concrete factor because the range between the maximum penalty and minimum penalty of different types of crimes varies. Moreover, it is more than a mathematic problem; it needs the action of legislature. With the help of java or other designs, we can have a program which helps the consistent identification of proof and the automatic findings in terms of sentencing. ACKNOWLEDGEMENT The work described in this paper was substantially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region (Project No.: 1-ZV7D). REFERENCES [1] [2]
[3] [4] [5] [6]
CONCLUSION AND FURTHER WORK
[7]
This study in the first analyzes the inherent nature of legal world, which is different from logical or mathematical world, and then discusses the different types of burden of proof and their corresponding test formula. It can be noticed that there exists apparent deviation in the proof beyond a reasonable doubt and proof on balance of probabilities in terms of their expressions. This phenomenon can be easily explicated by the introduction of epistemic modality, which is taken as indicating fact finder’s belief in the propositional truth. By taking rape cases in Hong Kong as an example, this analysis also elaborates the relevance of legal proof to the integrants of rape and factors affecting criminal liability or sentencing. So we can safely conclude that legal proof is different from proof in other fields or other concepts such as truth or reality in non-legal world because of its different criteria to rectify proof. This analysis, by providing a typological framework of certainty and an integrated framework to weigh proof in
[8] [9] [10] [11]
[12] [13] [14] [15] [16] [17]
5
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