Introduction
The case of Re A (Children) (Conjoined Twins: Surgical Separation) is one of the most ethically and legally challenging cases in English legal history. It concerned Jodie and Mary, conjoined twins, where the weaker twin, Mary, was entirely dependent on the stronger twin, Jodie, for her survival. Medical evidence was clear that without surgical separation, both twins would die within months. However, the separation operation would inevitably and immediately end Mary's life. The Court of Appeal was asked to declare whether the operation would be lawful. The court granted the declaration, but the three judges, Ward LJ, Brooke LJ, and Robert Walker LJ, provided different legal reasons for their decision. This makes identifying the ratio decidendi – the binding legal principle of the case – a complex task. This essay will argue that there is no single, clear ratio decidendi in Re A. Instead, the case offers several potential legal pathways. However, the most persuasive and legally significant reasoning, which comes closest to a ratio, is found in Brooke LJ’s judgment concerning the defence of necessity, though the most accurate ratio is likely a much narrower one, confined to the unique facts of the case.
Understanding Ratio Decidendi
Before analysing the judgments in Re A, it is necessary to understand the concept of ratio decidendi. In the English system of judicial precedent, the ratio decidendi (Latin for 'the reason for deciding') is the legal principle or rule that is essential to the judge's decision on the facts before them (Holland and Webb, 2019). It is this part of the judgment that is binding on lower courts in future cases with similar material facts. Anything else said by the judge, such as hypothetical scenarios or comments on other areas of law, is considered obiter dictum ('a thing said by the way') and is not binding, though it may be persuasive.
Identifying the ratio can be difficult, particularly when a case is heard by multiple judges who each give their own reasoned judgment, as was the situation in Re A. In such instances, one must look for a common legal principle agreed upon by the majority of the judges. If the judges agree on the outcome but for different reasons, it may be that there is no single binding ratio, or that the ratio must be extracted from the narrowest point of agreement that was necessary for the decision.
The Judgments in Re A
The Court of Appeal unanimously held that the operation to separate the twins would be lawful. However, each judge took a different route to arrive at this conclusion, creating difficulty in identifying a single binding principle.
First, Ward LJ approached the problem from the perspective of family law and the paramountcy of the child’s welfare, but acknowledged this had to be balanced against the criminal law implications. He considered the sanctity of life of both Jodie and Mary. He found that the operation could be justified using a novel application of self-defence. He proposed that the operation would be an act to defend Jodie from the threat to her life posed by Mary's continued dependence on her circulatory system. He framed it as Jodie, through the doctors, defending herself against the "passive" threat of Mary, concluding the operation was one of "quasi self-defence" ( Re A [2001] Fam 147, at 203).
Second, Brooke LJ provided the most structured analysis, focusing on the criminal law defence of necessity. He revived the test laid down by Sir James Stephen in his 19th-century Digest of the Criminal Law. According to Brooke LJ, the defence of necessity is available if three requirements are met: (1) the act is needed to avoid inevitable and irreparable evil; (2) no more should be done than is reasonably necessary for the purpose to be achieved; and (3) the evil inflicted must not be disproportionate to the evil avoided (Re A [2001] Fam 147, at 240). He systematically applied this test to the facts, concluding that the death of both twins was an irreparable evil, the operation was the only way to save Jodie, and the "lesser evil" was to save one life rather than lose both.
Third, Robert Walker LJ (as he then was) took a different approach, focusing on the doctors' intention. He was uncomfortable with the idea of the court authorising the positive act of killing. He argued that the operation's purpose was not to kill Mary, but to save Jodie. Mary's death would be a foreseen consequence of the operation, but not its primary purpose. This reasoning is similar to the doctrine of double effect, where an act with a good intention (saving Jodie) is permissible even if it has a foreseeable but unintended bad consequence (Mary's death). He concluded that because the "positive intention" was to save Jodie, there would be no "murderous intent" and therefore the operation would not constitute the crime of murder (Re A [2001] Fam 147, at 259).
The Search for the Ratio
Given these three different lines of reasoning, finding a common ratio is challenging. All three judges agreed on the outcome, but the legal grounds are distinct.
Ward LJ's 'quasi self-defence' argument is widely regarded as the weakest and least likely to form the ratio. As academics have noted, the concept of self-defence typically requires a defender to be responding to an unjust threat or attack (Herring, 2020). Mary was an innocent party, incapable of forming any intent, and her 'threat' to Jodie was simply a consequence of her existence. To apply self-defence in this context stretches the doctrine beyond its established limits and is unlikely to be followed. It is therefore best categorised as obiter dictum.
Robert Walker LJ's focus on intention and the doctrine of double effect is a more credible legal argument. It avoids confronting the idea that the law can authorise killing and aligns with other areas of medical law where treatment is withheld or withdrawn. However, it can be argued that severing the aorta common to both twins was a direct cause of Mary’s death, making it difficult to argue her death was merely a 'side-effect' rather than an intended part of the procedure to save Jodie (Brazier, 2001). While his reasoning is powerful, it was not explicitly adopted by the other judges, making it difficult to establish as the majority ratio.
This leaves Brooke LJ's analysis of necessity. His judgment is the most systematic and provides a clear, structured test. It directly confronts the dilemma and offers a potential defence within the criminal law. Many legal commentators see this revival and application of the defence of necessity as the most significant legal contribution of the case (Herring, 2020). It seems to be the most plausible candidate for a broader ratio: that the defence of necessity is available in exceptional medical cases where it meets the three-part test he outlined.
However, a more cautious and perhaps more accurate interpretation is that the ratio of Re A is extremely narrow and confined to its own unique facts. All three judges repeatedly stressed that their decision was made on the "unique" and "exceptional" circumstances of the case and should not be seen as creating a broad precedent for ending one life to save another. Therefore, the true ratio decidendi could be formulated very narrowly as: it is lawful for doctors to perform a surgical operation to separate conjoined twins which will result in the death of the weaker twin where (a) the twins will both die if the operation is not performed; (b) the weaker twin has no prospect of independent survival; and (c) the operation is in the best interests of the stronger twin who has the potential for a normal life. This fact-specific principle is the narrowest point of agreement necessary for the decision and is consistent with the court’s own warnings about the case's limited application.
Conclusion
In conclusion, the question of "what is the ratio decidendi of the conjoined twins case" does not have a simple answer. The presence of three separate and distinct judgments makes it impossible to identify a single, clear, and broad legal principle that commanded the support of the majority. Ward LJ's reasoning on self-defence is best seen as obiter. Robert Walker LJ's analysis of intention offers a compelling alternative but was not a basis shared by the others. The most influential reasoning came from Brooke LJ, whose structured application of the defence of necessity has been the focus of subsequent academic and judicial debate. This is the strongest candidate for a principle of wider importance. However, given the court’s explicit desire to limit the precedent, the most accurate ratio is a very narrow one, inextricably linked to the tragic and unique facts of Jodie and Mary's case. The case thus stands as a powerful example of the courts grappling with an impossible ethical dilemma, but its value as a binding precedent for future cases remains deliberately and necessarily limited.
References
Brazier, M. (2001) 'Not a case of killing'. The Guardian, 23 September.
Herring, J. (2020) Criminal Law: Text, Cases, and Materials. 9th edn. Oxford University Press.
Holland, J. and Webb, J. (2019) Learning Legal Rules: A Student's Guide to Legal Method and Reasoning. 10th edn. Oxford University Press.
Re A (Children) (Conjoined Twins: Surgical Separation) [2001] Fam 147.
