A definition of rationality (from tle Latin ratio, faculty of reason), useful also because it contains a gradation:
the subtler the differences and similarities one can see, the more one is rational;
the more one puts all eggs in one basket, the more one is irrational.
The terms reason and rationality have an ambiguity because in Italian the term reason implies that the purpose of the reasoning is being right in the sense of prevailing over: hence, prevailing over whom or what?
One thing is prevailing over problems in the sense of solving them to the benefit of all, quite another thing is prevailing over one's fellows in the sense of defeating and harming them to one's supposed benefit.
The definition of ethics as an objective in the Solutions & Proposals section solves this ambiguity conclusively: the ethical reason and rationality are those to the benefit of all. Actual benefit, not fake. Therefore non-ethical absence of reason and irrationality are those to the actual detriment of all.
From this definition of rationality derive increasing degrees of irrationality in illogicality:
Infinitely-valued logic on the wane: if the optimum rationality is that there exist infinite values, just like points in geometry, so that it is the values that correspond to facts as precisely as possible (and not the other way round as claimed by those who are either plain dumb or playing dumb), its decline is an ability to grasp an ever decreasing number of values. Example, in measuring something, switching from the callipers and the tenth of a millimetre, to the measuring tape and the centimetre, to the span.
Two-valued logic: there exist only two values, true or false, black or white, and any fact must correspond to either one of them. Example: "Either you are with us, or against us!" "Wait a moment, ..." "Then you're against us!"
Single-valued logic: there exists only one value, fixated, and any fact must correspond to it. Example: "Wear your woollens!" "But it's one hundred degrees!" "Just put it on!"
In this context it is essential to emphasise the factor known as "lumping everything together": the identification factor.
The word "identification" has two meanings, the second of which is less well known and almost the opposite of the first. Whilst the first means "to establish the identity of someone or something", the second means "to associate distinct people or things with one another to the extent of considering them to BE the same identity".
Whilst the first definition describes the act of distinguishing - that is realising that a certain someone or something is NOT someone or something else - the second describes precisely the opposite: NOT realising this distinction, considering on the contrary that a certain someone or something, and other distinct someone or something, ARE THE SAME someone or something!
Not just equal - which implies they are distinct - but the SAME entity: this is the leap into the abyss!
How many times have you heard people say: "men, women, this or that... ARE ALL THE SAME"? Whoever was saying this, at that moment, was on the verge of considering that all men, women, this or that... ARE THE SAME man, woman, this or that.
It is merely a matter of degree: they are thinking this way at a time when life is putting them under particular pressure, but all it takes is for them to find themselves in this state permanently for this consideration to become permanent, and for them to truly begin behaving accordingly.
Madness? Exactly.
Only, it's so deeply intervowen in day-to-day behaviours that it dnes'nt get recognised for what it is.
And, to paraphrase the saying, the road to hell is paved with such ensuing behaviours.