Rarely is the definition of a word more important than when it will determine the outcome of a murder trial. In a judgment released on 30th November, the Supreme Court provided important clarity for courts trying cases where diminished responsibility is raised as a defence.
In the case of R v Golds  UKSC 61, the Supreme Justices were tasked with determining what amounted to a ‘substantial’ mental impairment in the context of the defence of diminished responsibility. Under section 2 of the Homicide Act 1957 (as amended by the Coroners and Justice Act 2009), for the defence to succeed, it requires that the defendant’s ability to understand his own conduct, make rational judgments or exercise self-control was ‘substantially impaired’ by a recognised medical condition. If this is established (on the balance of probabilities), the verdict returned must be manslaughter. The sentence for the first is at the judge’s discretion and will almost certainly be much more lenient than the mandatory life-sentence for murder. The difference in the stigma attached to the two verdicts is obvious.
In Golds the Appellant asked seven Supreme Court justices to rule that ‘substantial’ means ‘something more than trivial’ (thus making the defence of diminished responsibility much easier for a defendant to prove in an appropriate case). The court robustly rejected this submission and instead stated that Judges should ask the jury to use their own common sense to determine the meaning of the word. However, if that will not suffice (either because the Judge feels more detail is required or because the definition has been raised in the case) the jury should be directed that the mental impairment being more than trivial is not alone sufficient for it to satisfy the requirements of the defence.
The judgment comes against a background of some confusion. In brief, the case of R v Egan  4 All ER 470 had stated (without the court having heard full argument) that the previous case of R v Lloyd  1 QB 175 legitimised two approaches to defining ‘substantial’ in the context of diminished responsibility. The first was to ask the jury to take a common sense view, the second was to define the term as:
“more than some trivial degree of impairment which does not make any appreciable difference to a person’s ability to control himself, but it means less than total impairment”
This interpretation (which, as the court commented had gained “some currency”) was the one that fell to be considered in this case.
Their lordships produced a single, unanimous judgment in Golds. This is useful in a case concerning the definition of a word where perceived difference of opinion between members of the court is highly likely. Equally, the thorough examination of the relevant case law (taking up 17 paragraphs of the 56 in the judgment) should provide much needed clarity on the issue.
At the heart of the judgment is a reaffirmation of the fundamental principle of English statutory interpretation – that ordinary English words contained in statute should be given their ordinary English meaning. As Lord Hughes succinctly put it: “the understandable itch of the lawyer to re-define needs to be resisted.” This is to be welcomed. There are various justifications for this principle but clarity and consistency are surely the most compelling. If statutory language was given specialist definitions by lawyers, the terms of any such definition would themselves fall prey to further interpretation, as would the resulting definitions and so on. A morass of conflicting interpretations would arise, themselves subject to potentially unending change. Both clarity and consistency over time would have been destroyed in one fell swoop.
Two other matters, touched on in Golds, bolster the importance of adhering to the plain and ordinary meaning of statutory terms. First, the court wished to ensure that if experts (ubiquitous in diminished responsibility cases) used the word ‘substantial’ it could be understood that they used it in the way the court had determined.
Second, a common-sense approach to language empowers the jury. The court pointed out that trial in this country is by jury not by expert. Whilst the court was here making the point that agreed psychiatric evidence should usually be accepted by the jury, to reaffirm the jury’s unfettered right to determine the meaning of ‘substantial’ must surely be welcomed.
Whilst the court decided that no direction on the meaning of substantial was necessary in most cases, it also had to decide what direction should be given in those minority of cases where a direction is given. Here, the court had to choose between two dictionary definitions of ‘substantial’. The first definition was “present rather than illusory or fanciful, thus having some substance” (the Egan analysis) and the second definition was something “important or weighty”.
The court preferred the second definition. In doing so it relied on a cogent analysis of the relevant authorities in which Egan was disapproved on the basis that the case had not been directly concerned with defining ‘substantial’ and had not heard full argument on the matter.
Overall, the case can be seen as a triumph for the traditional English legal principle of giving words their ordinary meaning and has firmly placed control of this concept in the hands of juries. The facts of diminished responsibility cases are both highly variable and often deeply tortuous. Situations in which the defence might be raised range from domestic violence (e.g. R v Simcox  Crim LR 402), sadistic sexually motivated attacks (R v Byrne  2 QB 396) and random killings by those inappropriately released from psychiatric hospital. In addition, degrees of planning vary almost as much as do impairments of mental functioning. To try and gloss the term ‘substantial’ in any way would make an already difficult task even more challenging.
In such circumstances, the safest course is to leave the definition of substantial to the collective wisdom of the jury (at least in the first instance). That way, necessarily flexible and imprecise legal concepts will be interpreted not through the narrow lens of lawyerly training and tradition but by the common sense of the citizenry at large. Far from being the lesser of two evils, such an outcome might be considered positively desirable.
 See para 43 of the Judgment.
 See Para 37 of the Judgment
 See Paragraph 42 of the Judgment
 See Paragraph 51