Stage 1: Whether the law differentiates

The first stage of the test considers whether the law prescribes different treatment for one group of individuals as against other groups. For example, in the 1998 High Court decision Taw Cheng Kong v. Public Prosecutor, Judge of Appeal M. Karthigesu found that the Prevention of Corruption Act^[21] differentiated between classes of people as it renders some, but not all, persons open to criminal prosecution in Singapore for offences committed outside Singapore.^[22]

While earlier cases expressed this stage of the test as a determination of whether a law is discriminatory, the Court of Appeal has warned against the confusing of the concepts of differentiation and discrimination. A differentiating law is one that draws distinctions between groups of people. A discriminatory law or executive act, on the other hand, is one that contravenes Article 12(1) and hence is unconstitutional.^[23] Therefore, the mere finding of a differentiating measure in this first stage does not necessarily make the law discriminatory, as the other two stages will still have to be taken into consideration. If the impugned statute does not contain such a differentiating measure, it is a good law and the objection fails.

Even if a differentiating measure is found, there is a strong presumption that it is constitutional. The legislature must necessarily have a wide power of classification in making laws that operate differently for different groups of people in order to give effect to its policy.^[24] Unless the law is plainly arbitrary, suggesting examples of arbitrariness are not ordinarily helpful in rebutting this presumption of constitutionality. It is presumed that Parliament knows best for its people, and is experienced in making laws directed at societal problems, hence its differentiation is based on adequate grounds. Therefore, to rebut this presumption it is necessary for the person challenging the law to adduce some material or factual evidence to show that it was enacted arbitrarily or had operated arbitrarily.^[25]

Stage 2: Intelligible differentia

The second stage of the rational nexus test looks at whether the basis for differentiation is founded on an intelligible differentia which distinguishes those who are grouped together from those left outside the group.^[26] To satisfy the second stage, there must be a discernible basis of classification. All persons being discriminated against by a law must share a common identifying mark that is not borne by those not discriminated against. Examples of such features include gender, age, race, religion, seniority of professional qualification and area of residence.^[27] Another feature that has been accepted by the courts as constituting an intelligible differentia is Singapore citizenship.^[22] Singling out a person or object with characteristics not peculiar to itself, but which may conceivably be found in other persons or objects, does not constitute classification.^[28] If there is no consistent means of identifying the persons treated differently, the differentiation is arbitrary and the law is invalid. If there is an intelligible differentia, the differentiation is not arbitrary in this sense and it is necessary to proceed to the third stage.

Equality under Article 12(1) does not require that all persons are treated alike, but rather that all persons in like situations should be treated alike.^[12] Similarly, failing to treat differently persons whose situations are significantly different also amounts to inequality. As such, at the second stage the question to be considered is whether persons falling within the same class are treated equally. Article 12(1) prohibits laws which require that some individuals within a single class should be treated more harshly than others.^[29] However, the law is not unconstitutional if all persons discriminated against are equally discriminated against, and all persons not discriminated against are equally not discriminated against.^[27] The courts have found this stage to be satisfied where under a statute all citizens are equally liable to prosecution, whereas all non-citizens are equally immune from it.^[22] The second stage test was also found to have been satisfied where all members of the Singapore Congregation of Jehovah's Witnesses found to have been in violation of the Societies Act^[30] were treated equally.^[31]

Stage 3: Reasonable relation to statutory objective

In this stage, it is necessary to inquire into, firstly, the object of the statute, and secondly, whether the basis of differentiation against or for a particular class is a reasonable means of achieving such an object. The essence of the test is whether it is reasonable, taking into consideration the object of the statute, to distinguish between persons on the selected basis of differentiation. As such, it is necessary to ask how the differentiation against or for one particular class furthers the object of the statute.^[27] The law is not arbitrary if the basis for discrimination has a rational relation to the object sought to be achieved, and the statute will be declared valid and constitutional.

In Taw Cheng Kong, the respondent challenged his conviction for corruption on the ground that section 37 of the Prevention of Corruption Act,^[21] which extends the effect of the Act to corrupt acts by Singapore citizens (but not non-citizens) occurring outside Singapore, discriminated against citizens and thus violated Article 12(1). The Court of Appeal held that the distinction drawn by the section 37 between citizens and non-citizens who are abroad is valid as it is a reasonable means of achieving the Act's object, which is to address acts of corruption taking place outside Singapore but affecting events within it. The exclusion of non-citizens from the ambit of section 37 observes international comity and the sovereignty of other nations.^[32]

Unreasonable legislative objectives

In equal protection cases, the purpose of the law must be distilled before the reasonableness of a classification can be judged. When the purpose of the law is not explicitly stated, the court may conclude that there is no legitimate public purpose, assume that there is a legitimate public purpose but refuse to look for it, or draw some inferences as to what it is. When the purpose of the law is explicitly stated, the court may either accept it at face value; or challenge the integrity of the legislative declaration, looking behind the explicit purpose to determine the true purpose. In the latter situation, what is concerned is the discriminatory character of the legislation. The need to identify the legislative purpose has been said to involve the court in the "thornier aspects of judicial review", because it must either "uncritically and often unrealistically accept a legislative avowal at face value" or "challenge legislative integrity and push beyond the express statement into unconfined realms of inference". The court must then "make a judgment as to the purity of legislative motive and ... determine the legitimacy of the end".^[33]

This step is necessary because the rational nexus test is not foolproof. The test is based on the presumption that the legislative object itself is not in violation of the Constitution. However, if the object of the statute is itself illegitimate, a classification may be invalid even if it satisfies the test. Hence, the test is only applicable if the object of the impugned legislation is a proper one.^[34]

In India, a solution was proffered by means of a more holistic approach to the constitutional promise of equality. In Maneka Gandhi v. Union of India (1978),^[35] the learned Justice Prafullachandra Natwarlal Bhagwati noted that "an essential element of equality pervades Article 14", the equivalent of Singapore's Article 12. With that as a starting point, he went on to assert that "the procedure ... must be right and just and fair and not arbitrary". The judge in Maneka Gandhi therefore spoke for a dynamic approach to equality, one that should not be "subjected to a narrow, pedantic or lexicographic approach".^[36] This more liberal approach, which accords courts the latitude to deal with legislation backed by arbitrary or unreasonable objectives, was cited with approval in Malaysia by the learned Judge of the Court of Appeal Gopal Sri Ram in Tan Tek Seng v. Suruhanjaya Perkhidmatan Pendidikan (1996).^[37] It is unclear, though, if this test will be applied in Singapore due to a dearth of case law on the matter.

Over- and under-inclusiveness

Another problem encountered when applying the rational nexus test is that of over- and under-inclusiveness. Under-inclusiveness occurs when the legislative classification fails to embrace all persons within the ambit of the objective sought to be achieved by the law.^[38] On the other hand, over-inclusiveness occurs when the classification not only embraces persons within the ambit of the legislative objective, but also persons outside it.^[39] Both over- and under-inclusiveness are currently tolerated in Singapore under the rational nexus test, as a classification can still bear a rational relation to the legislative objective notwithstanding that it embraces more or less persons than its object requires.

It has been argued that this results in the different treatment of persons in like situations, and thus violates Article 12(1). Although a rational connection exists between the classification adopted and the legislative object, the effect of an under-inclusive classification is to accord different treatment to persons similarly placed.^[38] However, the courts have often justified under-inclusiveness on the ground that the legislature is free to recognize degrees of harm, to confine its restrictions to cases where the need is felt to be the greatest, and to advance its policies step by step.^[40] Despite this, resort to legislative wisdom to justify under-inclusiveness, if used indiscriminately, may result in the watering down of the equal protection guarantee provided by Article 12(1).

Similarly, where an over-inclusive classification is concerned, a rational relation still exists between the differentia adopted and the legislative object. Thus, it is tolerated under the rational nexus test in Singapore. While the effect of an over-inclusive classification may be to accord similar treatment to persons differently placed,^[39] courts have nonetheless justified it on the ground that the exigencies of the situation require such classification. The US Supreme Court case Hirabayashi v. United States (1943)^[41] is an example of this principle. Following the Japanese attack on Pearl Harbor on 7 December 1941, President Franklin D. Roosevelt issued an executive order requiring, among other things, all persons of Japanese ancestry within a designated military area to be "within their place of residence between the hours of 8 p.m. and 6 a.m." and to report to the authorities to register for removal from the military area. The defendant, Gordon Hirabayashi, was convicted of violating the curfew and the registration requirement. The order was arguably over-inclusive as it did not distinguish between Japanese Americans who were loyal to the US and those in respect of which there was evidence of disloyalty. Although the Court noted that distinctions between citizens solely on the basis of ancestry "are, by their very nature, odious to a free people whose institutions are founded upon the doctrine of equality",^[42] because the US was at war with Japan the race-based classification bore a rational relation to the aim of the order, which was to protect from sabotage war materials and utilities in areas believed to be in danger of Japanese invasion and air attack. The Court said: "We cannot close our eyes to the fact, demonstrated by experience, that, in time of war, residents having ethnic affiliations with an invading enemy may be a greater source of danger than those of a different ancestry."^[43]

In Taw Cheng Kong, the High Court was of the view that section 37(1) of the Prevention of Corruption Act was both under- and over-inclusive. It did not apply to non-Singapore citizens such as permanent residents and foreigners working for the Government who received bribes for acts which would be done in Singapore. On the other hand, it would catch a Singapore citizen now a foreign permanent resident employed in a foreign country by a foreign government who received a bribe in relation to a transaction that had nothing to do with Singapore. For this reason, Karthigesu J. found section 37(1) to be unconstitutional since the nexus between the classification and section 37(1)'s objective was not reasonable enough to justify derogating from Article 12(1).^[44] The High Court's decision was reversed by the Court of Appeal, which held that the under-inclusiveness was not fatal because of the "overriding need to observe international comity". In any case, "[t]he enactment of a provision need not be seamless and perfect to cover every contingency. Such a demand would be legislatively impractical, if not impossible." The over-inclusiveness of section 37(1) was deemed irrelevant to the constitutional issue because the provision applied equally to all Singapore citizens.^[45]

Three-tiered scrutiny

In footnote 4 of United States v. Carolene Products Co. (1938),^[55] Justice Harlan F. Stone opined that where legislation was aimed at "discrete and insular minorities" who lack the normal protections of the political process, a more exacting standard of judicial review with no presumption of constitutionality should be applied.

At present in the United States there are three different levels of scrutiny. Firstly, if a law categorizes on the basis of race or national origin (which are regarded as suspect classifications), or infringes a fundamental right, strict scrutiny is applied. Accordingly, the law is unconstitutional unless it is narrowly tailored to serve a compelling government interest.^[56] In addition, there should not be a less restrictive alternative available to achieve that compelling interest. Secondly, if the law categorizes on the basis of gender, legitimacy or similar quasi-suspect classifications, intermediate scrutiny is applied – the law is unconstitutional unless it is substantially related to an important government interest.^[57] Finally, the traditional rational basis review is applied if the law categorizes on some other, non-suspect, basis. In this case, the law is constitutional so long as it is reasonably related to a legitimate government interest.^[58]

In Malaysian Bar v. Government of Malaysia (1987), the Supreme Court of Malaysia referred to the strict scrutiny approach but asserted that in reality it was not very different from the traditional rational nexus standard, which it then proceeded to apply. The Court's endorsement of strict scrutiny was much less ambiguous in Government of Malaysia v. V.R. Menon (1990).^[59] It held that the impugned Act was concerned with economic and social welfare and not fundamental rights, and therefore the trial judge had erred in applying a stricter standard of review. As such, the court implicitly endorsed the application of the strict scrutiny test in cases concerning fundamental rights in Malaysia.

There are several criticisms of the three-tiered scrutiny analysis, the most compelling reason against its adoption arguably being that it does not control judicial discretion: the identification of classifications as suspect, quasi-suspect or non-suspect involves unconstrained balancing of public and private interests, and political and social interests.^[60]

Test of proportionality

The test of proportionality in English law, which is applied to determine whether a fundamental right is appropriately restricted by legislation, has three limbs:^[61]

1. The legislative objective must be sufficiently important to justify limiting the fundamental right.
2. The measures designed to meet the legislative objective must be rationally connected to it.
3. The means used to impair the right must be no more than is necessary to accomplish the objective.

It has been suggested that a proportionality analysis better safeguards equality compared to the American three-tiered scrutiny approach.^[62] The third limb of the proportionality test may also serve to strike down over-inclusive classifications which are currently tolerated under the rational nexus test.

Test of reasonableness

In Maneka Gandhi,^[35] Bhagwati J. appeared to suggest that the rational nexus test should not be applied to Article 14 of the Indian Constitution, which guarantees equality before the law and equal protection of the law, because it led to a narrow and pedantic interpretation of the provision. He held that Article 14 should not be construed too narrowly as it was the pillar on which the foundation of the Indian Democratic Republic rested. In his view, the principle of reasonableness was an essential element of equality or non-arbitrariness, and it pervaded Article 14 "like a brooding omnipresence".^[63]

A test of reasonableness was applied to Article 8(1) of the Malaysian Constitution in some cases,^[64] but it was later rejected by the Federal Court in Danaharta Urus Sdn. Bhd. v. Kekatong Sdn. Bhd. (2004). The Court noted that in cases subsequent to Maneka Gandhi the reasonable classification test had been applied, even by Bhagwati J. himself.^[65] Furthermore, equality under Article 8(1) does not mean absolute equality, but only assures the right to equal treatment with other individuals in similar circumstances.^[29] The rational nexus test is needed to determine if a law applies equally to all persons in the same group, and is therefore an "integral part" of Article 8(1).^[66]