Legal certainty requires a balance between stability and flexibility. Following the hermeneutical footsteps of legal theorists such as Aulis Aarnio and Alexander Peczenik, a distinction can be made between formal and substantive legal certainty; between predictability and acceptability of legal decision-making. Formal legal certainty implies that laws and, in particular, adjudication must be predictable: laws must satisfy requirements of clarity, stability, and intelligibility so that those concerned can with relative accuracy calculate the legal consequences of their actions as well as the outcome of legal proceedings. Substantive legal certainty, then, is related to the rational acceptability of legal decision-making. In this sense, it is not sufficient that laws and adjudication are predictable: they must also be accepted by the legal community in question.