The law must be ascertainable. This is a requirement for the enforceability of enacted law and for the validity of common law. In jurisdictions where the common law creates offences, it must be possible to find out what they are.
It doesn't matter how sure we now are of what the common law used to be, if it was uncertain when a person did acts that are now alleged to have been contrary to that law.
In PGA v The Queen [2012] HCA 21 (30 May 2012) the issue was whether in 1963 in South Australia, where rape was a common law crime, a wife could withdraw her consent to sexual intercourse with her husband.
To find that out, one would think that it would be sufficient to consult the case law of the time. Were husbands charged with raping their wives? Did judges say that that was rape? What did legal scholars think? If a man went to his lawyer then and asked, what would he have been told?
According to the majority in PGA, a lawyer back then would have concluded that a wife could withdraw her consent to sexual intercourse with her husband. This view would have been reached by considering the fact that marriage is not permanent [59], that marriage is a consensual contract which could be breached by wilful and persistent refusal of sexual relations – implying that some refusal is possible [60], that relevant legislation required cohabitation but did not require matrimonial intercourse as an order to that effect would be unenforceable [60], that a wife had a distinct legal personality from her husband, particularly as to property rights, and this undermined any idea of her being her husband's property [61], and that women had the vote and had recognised rights to commercial and professional lives [60]-[61].
These considerations, according to the majority reasoning, would have led a lawyer in 1963 to advise that a husband could be guilty of raping his wife.
It is for judges or the legislature to change the common law. The majority review at [19]-[24] the meaning of the term "the common law", emphasising how judicial precedents may diminish in value over time. Old decisions can become obsolete and inoperative.
But, one would have thought, it is for judges to say when that obsolescence and inoperativeness has led to a change in the common law, and to declare the new law for the future. The majority in PGA have made that declaration retrospectively. One does not have to say that they are wrong in deciding that a judge in 1963 would have made the same declaration, to recognise the injustice from the point of view of the defendant who now faces historical charges including two counts of rape of his then wife.
Our natural aversion to rape may cloud perception of this injustice. If it was reasonably likely that in 1963 a husband would have been advised that as far as the law was concerned he was entitled to sexual intercourse with his wife because there was no judicial decision to the contrary, the new law was not ascertainable. A court that changed the law, or at least made it ascertainable, should only do so prospectively, acquitting this defendant but making the law clear from then on. Enacted law is "law" if properly enacted, but if it is not reasonably ascertainable it will be unenforceable, whereas common law must be ascertainable in order to be "law". If enacted criminal law is not ascertainable a prosecution should be stayed: Christian v R (The Pitcairn Islands) [2006] UKPC 47 at [24] (not cited in PGA):
"Their Lordships would accept that the fact that a law had not been published and could not reasonably have been known to exist may be a ground for staying a prosecution for contravention of that law as an abuse of process... .",
The ECtHR has upheld convictions where retrospective change in the law has been reasonably foreseeable, as in the removal of the marital exemption defence to rape, upholding R v R [1992] 1 AC 599: SW and CR v UK (1996) 21 E.H.R.R. 363. It may be that with increasing focus on the idea of the rule of law this tolerance of injustice to the defendant whose prosecution marked the change in the law will diminish. The traditional view that judges declare the common law as it has been from time immemorial is now regarded as an outdated legal fiction.
Just as reasonable minds may differ on the application of known law to the facts of a case, so too may reasonable minds differ over how and when the common law may change. An obligation to obey law that has not yet been declared is a form of "common law" not within the definitions recognised by the majority in PGA. It is unjust.
There is plenty of authority for this, as Heydon and Bell JJ demonstrate in their dissenting judgments. A helpful summary from the House of Lords is in R v Rimmington [2005] UKHL 63 especially at [33] which concludes:
"There are two guiding principles: no one should be punished under a law unless it is sufficiently clear and certain to enable him to know what conduct is forbidden before he does it; and no one should be punished for any act which was not clearly and ascertainably punishable when the act was done. If the ambit of a common law offence is to be enlarged, it "must be done step by step on a case by case basis and not with one large leap": R v Clark (Mark) [2003] EWCA Crim 991, [2003] 2 Cr App R 363, para 13."
There is a risk of cherry-picking authorities in this sort of argument, but I recommend Rogers v Tennessee, 532 U.S. 451 (2001) as an illustration of the upholding of a common law change but only where there had been a pervasive change in the law that should have put the defendant on notice that the law was clearly going to change. The change was not unfair or arbitrary. Scalia J dissented on the grounds that restrictions on legislative retrospective change should also apply to retrospective common law change. But even on the majority view there is a requirement of ascertainability before a defendant is bound by future decisions changing the common law.
Anyway, this interesting case raises questions about who defines the common law, is it just social mores or does it have to be declared by judges, whether retrospective effect should be more acceptable for common law offences than for legislated offences, and the extent to which social and legislative changes in some areas can influence assumptions about the common law in other areas. In New Zealand we have only one common law offence - some forms of contempt of court - but we do have common law defences. It was not until as recently as 1986 that legislation removed the spousal immunity defence to rape, which implies that it did exist at common law (at least in a form that had been modified by earlier legislation) until then. Some people think we are behind Australia in our development, but - as one who can remember 1963 and the grassy knoll quite clearly - I don't think that in 1986 we were 23 years behind.
