To know if a possible amnesty law for the benefit of those investigated and convicted in the so-called cause of the procés violates our rule of law or not, the first thing would be to properly define what is a rule of law, what are their configurative characteristics and what relationship they have with a democracy worthy of that name. This will also help us to clarify a further issue, which is the possible unconstitutionality of the initiative, from the moment in which our Constitution affirms in its article 1.1 that “Spain is constituted as a social and democratic state of law, that advocates as superior values of its legal system freedom, justice, equality and political pluralism.”
To specify the features that make up a genuine rule of law is certainly not a peaceful issue. From a certain (positivist) point of view, every state is by definition a rule of law. And this is because, as Ihering said, “so right is that which commands universal education, as that which prohibits blacks from reading and writing” . But the truth is that, for some time now, it has been agreed to call the rule of law only that State whose normative production meets a series of characteristics that prohibit the arbitrary exercise of power and guarantee the freedom, security and equality of citizens.
On what these characteristics are there are many theories, which we could group into two big blocks: The thick and the thin (thick and thin). Thick theories include concepts such as justice and respect for human rights, as well as plural and democratic participation in the elaboration of norms. It is true that it is difficult to dispense with such values in order to define a genuine rule of law. Here, however, we will follow the supporters of the thin conception, who try to limit themselves to a more formal or procedural analysis, without substantive values. And not because they do not consider them important, but because they understand that formal ones are enough. Among other reasons, because it is very difficult or impossible to cite in practice an example of a State that complies with the procedures and materials. In any case, thin requirements would constitute that lowest common denominator without which we cannot properly speak of the rule of law.
The two authors that constitute the fundamental reference of the thin stream are Leon Fuller And Cass Sunstein. If we were to synthesize their lists of principles or requirements into one we could only formulate the following:
1.- The law must be formulated in general rules.
2.- The rules must be prospective and not retroactive.
3.- There must be a congruence between the promulgated and the applied law.
4.- They must be clear, not contradictory and not demand the impossible.
5.- They must be stable.
6.- There must be a separation between the normative elaboration and the application of the law, with the right of hearing and appeal before independent bodies.
These are inexcusable requirements if we intend to treat the recipients of the rules as true citizens, that is, as autonomous and responsible beings capable of understanding and following rules, as one might expect in a democracy worthy of the name, and not as mere subjects devoid of dignity (Fuller). Well, an amnesty law such as the one raised raises doubts about at least four (1,2,3 and 6) of the six requirements stated. Let’s look at it in more detail.
With the formulation of the requirement of the generality of the norm, it is asked that it be a question simply of that: Of a rule and not of a casuistic decision of a controversy that thinks only in a certain matter (Fuller). A rule is associated with the idea of impersonality, impartiality, and interdiction of arbitrariness (Sunstein). Consider only abstract situations and not concrete people. This idea connects with a fundamental principle of our legal tradition, already clearly formulated by the Romans in the Law of the XII Tables (451 BC), which is the prohibition of privilege (privus legis means exempt from law). Commenting on the rule, Cicero wondered “what could be more unfair than that, since the law, by its very essence, must be a resolution and a mandate for all.”
There is no doubt that an amnesty clearly violates this fundamental principle, as it consists of a law whose purpose is to exempt certain persons from the application of others. But the violation would be especially serious if it were granted without consideration other than support for an investiture, without regret or unconditional commitment to future subjection to the violated rules, because in that case the exception would be even more radical.
The requirement of non-retroactivity is more complex, but it is thinking of rules that seek to attend exclusively to past situations, and not rules that affect them indirectly as a result of its claim to regulate future situations. In other words, it is one thing to lower the penalty for a crime in the future, but it has as a necessary reflex effect to reduce the penalty of those committed previously, and another very different one is a rule that seeks to affect only the past penalties but leaving the future ones unchanged. Fuller puts as an example of this type of regulation the law enacted by the German parliament after the purge of Röhm (“The Night of the Long Knives”) that turned these murders into legal executions.
There is no doubt that the amnesty we are discussing is closer to this second type of rules than to the first ones, because somehow it comes to legalize, by leaving without sanction of any kind, the unconstitutional and criminal acts carried out during the procés.
Under the requirement of congruence between promulgated and applied law, the idea is invoked that the law in books must coincide with the law in the street. If the promulgated right says one thing, but does not apply to anyone, or some are exonerated for no further reason that they can buy that privilege at a price that others cannot afford, depending on the concurrent circumstances in each case, The rule of law is then compromised in its principles of generality and predictability (Sunstein).
Finally, with the requirement of separation between the normative elaboration and the application of the law, it is a question of avoiding, both that those who implement the norm modify it (Sunstein), and that those who promulgate it decide later its modification or non-application depending on the specific case. This idea refers to another more principal one, that of the separation of powers, which, in essence – and despite the general misunderstanding in this regard – it aims to preserve the principle of supremacy of democratic law.
It seems evident that with the proposed amnesty, what is intended is precisely to remove from the judiciary the execution of the criminal law in order to exempt its application in that case, but leaving it unchanged for everyone else.
A logical consequence of all the above (although perhaps not the most important thing) is that an amnesty law formulated in these terms does not seem very compatible with a Constitution whose first article defines the State as of law, and that, to a greater extent, the law of the State. it does not expressly admit it in its article.
 R.. Ihering, Law as a Means to an End, I, 1877.
 The Morality of Law, 1969.
 Legal Reasoning and Political Conflict, 1996.