I posed the question in title in an earlier post on this blog. In an article published in the current issue of the International Journal of Constitutional Law, Liav Orgad provides one possible answer. Here is the abstract:
From Plato’s Laws through common law and until modern legal systems, preambles to constitutions have played an important role in law and policy making. Through a qualitative analysis of the legal status of preambles in different common law and civil law countries, the article highlights a recent trend in comparative constitutional law: the growing use of preambles in constitutional adjudication and constitutional design. The article also explores the theory of preambles and their functions. It examines the legal status of the U.S. preamble and shows how the U.S. preamble remains the most neglected section in American constitutional theory. The article then presents a typology for determining the legal status of preambles: a symbolic preamble, an interpretive preamble, and a substantive preamble. While focusing on Macedonia, Israel, Australia, and the Treaty of Lisbon, the article discusses the sociological function of preambles in top-down and bottom-up constitutional designs.
An earlier version is available on SSRN. It’s a fascinating piece, as applicable to the preamble to the Irish Constitution as it is to those discussed by Orgad. As he notes, “courts have been invoking the Preamble in order to interpret the Irish Constitution and as a guiding tool to understand its spirit and values”. Indeed, there is a long tradition of making use of the preamble in the interpretation of the provisions of the Constitution, from McGee v AG  IESC 2,  IR 284 (19 December 1973) and Norris v AG  IESC 3,  IR 36 (22 April 1983) through McGimpsey v Ireland  IESC 3,  IR 567 (1 March 1990), AG v X  IESC 1,  1 IR 1 (5 March 1992) and In re Article 26 and the Regulation of Information (Services outside the State for the Termination of Pregnancies) Bill 1995  IESC 9,  1 IR 1 (12 May 1995) to Laurentiu v Minister for Justice  IESC 47,  4 IR 26 (20 May 1999) and A v The Governor of Arbour Hill Prison  IESC 45,  4 IR 88 (10 July 2006).
In that last case, Murray CJ said:
The Constitution like others, is holistic, provides a full and complete framework for the functioning of a democratic State and an ordered society in accordance with the rule of law, the due administration of justice and the interests of the common good. In providing for the common good and seeking “to attain true social order”, in the words of the preamble, the application of the Constitution cannot be distorted by focusing on one principle or tenet to the exclusion of all others. …
Certainly, issues concerning the constitutionality of statutes are on a plane higher than the mere common law, they concern questions fundamental to the rule of law, the protection of rights and the very framework within which, in the words of the preamble to the Constitution, “true social order is attained”. Normally those fundamental constitutional concepts, such as the rule of law, individual rights, justice and a social order based on that rule of law blend together so that the principles of constitutional justice to be applied to resolve issues can be readily deduced. On other occasions some of those considerations may be competing or even conflicting ones, where the Courts have to balance those different interests so as to do justice within the framework of the Constitution.
This is the task conferred on constitutional courts.
Denham J commented:
The Constitution established the power of constitutional review by the Superior Courts which, as with all powers and duties, is required to be performed constitutionally. Thus, it must be exercised in a manner consistent with the Constitution, harmoniously with other (and sometimes conflicting) rights and principles, and “seeking to promote the common good”: as the Preamble states.
And Hardiman J held:
In CC v Ireland  IESC 48,  4 IR 1 (12 July 2005) I cited a passage from O’Higgins CJ in The State (Healy) v Donoghue  IR 325 which also seems relevant here:
In the first place the concept of justice, which is specifically referred to in the preamble in relation to the freedom and dignity of the individual appears again in the provisions of Article 34 which deals with the Courts. It is justice which is to be administered in the Courts and this concept of justice must import not only fairness and fair procedures, but also regard to the dignity of the individual. No court under the Constitution has jurisdiction to act contrary to justice.
… each of the factors enumerated may, in an appropriate case, be central in the protection of the rights of others, or of the community as a whole, as well as those of the applicant. To put this another way, they may in an appropriate case be central to the achievement of the common good and of that Justice and true social order prominently mentioned in the Preamble to the Constitution, …
… the closure, solace and vindication … accorded to a victim of a grave crime, and … true social order [are, h]aving regard to the terms of the Preamble to the Constitution and of Article 40.3.1 and 2 … constitutional interests requiring … vindication by the Courts in an appropriate case.