Normality is the distinction between normal and deviant (Luhmann, Risk: A Sociological Theory). It is a difference not a thing-in-itself. This distinction serves as an instrument for observing society. This is, among other things, an evolutionary deviation from the old good/evil distinction.
Rationality or the notion of the rational is the distinction between rational and emotional (or passionate). It doesn’t help to call it a distinction between rational and irrational (or non-rational) because that makes irrational or non-rational just an absence of the rational.
The word normal signifies a particular kind of difference; it doesn’t name anything real in itself. The same goes for the signifier rational. So if we speak of “the normal” or “the rational” we are referring to differences, not any kind of essence.
The OED gives this definition of rational:
a. Having the faculty of reasoning; endowed with reason. Esp. in rational being, rational creature, rational soul, etc.
The first entry for rational in the OED is from 1398
J. Trevisa tr. Bartholomaeus Anglicus De Proprietatibus Rerum (BL Add.) f. 330 Þe cercle tokeneþ þe soule racional.
Classical ontology would call the modifiers normal and rational qualities or properties, rather than substances. But these adjectives were later nominalized as normality and rationality, with rationality being a thing that mankind possesses, a trait.
The first use of rationality comes from mathematics.
The first entry is a from an English translation of Euclid’s Elements of Geometry:
1570 H. Billingsley in tr. Euclid Elements Geom. x. f. 246v These wordes in length and in power are neuer referred to rationalitie or irrationalitie.
1598 [implied in: A. M. tr. J. Guillemeau Frenche Chirurg. 50/2 Thervnto are many thinges reqvired, which I heere normallye and rightlye will prosecute.
1706 Eng. Scholar Compl. 90/2 Normal, exact, according to Rule.
a. The character or state of being normal.
1839 Morning Chron. 30 May The blistering demon of normality is evoked from the hell of French infidelity to become the patron saint of high-Church educators.
But getting back to Luhmann and risk, if the future cannot be known, all we have are expectations, and these expectations can be fulfilled or disappointed. The normal is the expected, and the deviant is the unexpected or surprising event. To deal with undesirable surprises, modern society has invented things like risk mitigation, risk reduction, risk management, risk analysis. These tools are ways to rationalize systems, like the economy, or make a system less random. Part of risk management is the invention of contingency planning: If X unfortunately occurs, we do Y. Ideally, not much thinking is necessary when X happens; you simply carry out the contingency plan (Y). So when we have something that is apparently “nonrational,” like earthquakes (or other “acts of God”), that at some point might happen, we enhance the sense of rationality, stability, or regularity. A social system can expect earthquakes to happen when particular people are busy with other things and thinking about earthquakes. Rituals serve the same purpose (stabilizing or rationalizing the future): If someone dies, we have the body taken away and start making funeral arrangements. No real decision is required, which reduces the probability of making a bad decision.
If we can rationalize one system through contingency planning, then we can minimize possible disturbance to other systems. The greater the number of decisions that have to be made, the greater to probability of bad outcomes.
Julien Freund defines rationalization as “the organization of life through a division and coordination of activities on the basis of exact study of men’s relations with each other, with their tools and their environment, for the purpose of achieving greater efficiency and productivity.” (Freund, Julien, 1968. The Sociology of Max Weber)