There are two fundamental approaches to defining something: The first is to define something as a result of itself (boiling water is water that has boiled). The second, is to define something as the consequence of something other than itself (boiling water is the result of applying certain heat to water).
The first way of defining something uses data that occurs after the effect has occurred (Ah, the water has boiled, so it must be boiling water) and extrapolates what could be considered “cause” after the fact. The second, uses data that is thought to be predictive of the effect, which data occurs before that effect happens (Ah, I heated the water and, look, I have boiling water).
The difference between the two approaches to defining something is a little more complex that these examples, of course. But for now, I think its an adequate start to a discussion of the basis of how people come up with definitions of the rule of law.
Those defining the rule of law using the first approach, treat the concept as an ideal type and then describe that ideal type by referring to various suitable and observable correlates of that ideal type. For example, “the rule of law is a characteristic of an ideal, civilized democratic society which respects human rights, evinces good governance, has regular elections, and so on”. Once described, you of course have the variables implicit in that description itself as a measure of that ideal, and the inherent methodology to vary the expression of that ideal is, of course, by manipulating those correlative variables so they align with the measure of those correlative variables in circumstances where that ideal is “reached”.
Those defining the rule of law using the second approach likewise start off defining it as an ideal type. This may well be identical to the definition of someone utilising the first approach. Or, it may be something different such as, “humans are evolutionarily gregarious and so live in groups, and the rule of law is a mechanism to facilitate the success of that co-habitation”.
However, in the second approach, once the concept is defined, the definitional components of the definition are not treated as variables which prove the existence of the phenomenon itself. Instead, the second approach – by way of reason, logic and rationality – requires that potential prior causes preceding the expression of those definitional components that are taken to define the rule of law be identified, and then scientific methodology be used to prove or disprove the hypothesized causal relationship between those hypothetical causes and the definitional component variables describing the rule of law.
It goes without saying (to skip the 1960’s type debates that are so well done elsewhere) that both approaches to defining something of course have their use cases, and are extensively used in various fields of human endeavour. Defining something through one or more correlative variables just cannot be avoided where there are no indications as to the cause of the phenomenon. And the often impossible complexities of trying to influence a correlative relationship once it has been identified often demands that scientific methodology is applied to ascertain whether in fact there is a causative relationship between correlates, or not.
However, although in fact both approaches should be working hand in glove, in the field of the rule of law, unfortunately, there the correlative studies hold sway. The vast, vast majority of expressed opinion on the rule of law, its demise and maintenance are based on correlative approaches. There are virtually no studies based on the causative model, which focuses on how identifying and researching the effect of manipulating variables can influence the expression of the rule of law.
There are ready reasons explaining this concentration of a correlative approach to the rule of law, over a scientific approach. I mean, why waste time looking for prior causative factors when trying to deal with the terrible consequences of a breakdown of the rule of law once it has occurred? When trying to bring particular monsters to book? When trying to create some order in the chaos following the breakdown in the rule of law, by modelling that order on societies were the rule of law is holding?
However, the flip side of not looking at causative factors related to the rule of law is, I think, that there are a myriad of opinions out there all with different, almost personalized definitions, of what the rule of law is, which focus almost exclusive on how to rectify its breakdown once it has fallen apart rather than on its maintenance, and a bazillions funds doing down the drain in unsuccessful efforts to re-establish and maintain the rule of law because the mechanics of the rule of law are so poorly understood from a causative perspective.
What is needed, really, is to counter-balance the preponderance of efforts based on the correlative approach, with an increase in causative analysis based on rationality, reason and logic, and sound scientific research methodology, to identify the mechanics of the rule of law and its establishment, maintenance and breakdown, through research that tests causal relationships between observable and measurable variables hypothesized as outcomes of the rule of law.