The principle of intergenerational equity is a particularly significant contribution to sustainability jurisprudence. This principle argues that the current generation is the trustee of the natural environment, and assumes a fiduciary responsibility for the ecological integrity and viability of environment for subsequent generations.2 The principle incorporates long-term, transgenerational thinking into legal reasoning – it provides a necessary counterweight to the short-termism that is the hallmark of political and economic decision-making. The principle of intergenerational equity has been recognised in international law, as embodied in influential soft law texts such as the Rio Declaration on Environment and Development (1992) and the United Nations Framework Convention on Climate Change (1992). Such documents express the moral and legal obligation to take into account the rights of the unborn and the needs of future generations, thus extending the range of environmental governance. The principle of intergenerational equity has also been expressed robustly within domestic constitutional jurisprudence. A key example includes the Oposa v. Factoran (1993) Supreme Court Ruling in the Philippines,3 in which the Court found that a group of children had standing to sue the government for failing to protect forest resources for the ultimate benefit of future generations.4 By validating intergenerational standing, the Court achieved the incorporation of this principle into constitutional environmental law and described how domestic courts can operationalise vague international norms into specific legal orders. These cases demonstrate how constitutional forms of intergenerational equity can become an institutional fixture of environmental rights, where durability and the prudent capacity to look forward are valued in the operation of legal systems.

Also important in the normative architecture of sustainability are the precautionary and preventive principle(s).5 By highlighting and shifting the focus of environmental law away from immediately reactive governance, the precautionary and preventive principles model a proactive approach to governance that obliges states to fore-know a potential ecological harm and avoid it before it materialises. The precautionary principle allows for administration or judicial action notwithstanding environmental risk on full scientific certainty, while the preventive principle implicitly obliges environmental harm to be avoided altogether, rather than merely reduced afterwards. Together, these principles encourage a normative legal culture that favours ecological resilience over economic opportunity.

In the context of constitutional law, these principles have the potential to be transformative. They justify judicial action before any environmental damage is done, giving the judiciary greater power to act as a guardian of environmental quality. These principles also shift the burden of proof in favour of those wishing to engage in a potentially damaging activity. Developers or state actors will need to show that their action will not have a serious risk to the environment rather than the other way around. In practice, this has been utilised to support constitutional challenges to large-scale infrastructure or extractive projects on the basis of serious ecological risk and potential for irreversible ecological damages. In situations where these principles are enshrined in constitutional text or recognised by a court interpreting constitutional text, they constitute a more risk-averse, precautionary, and ecologically responsible legal order.6