Throughout the rest of the book, Lewis goes on to counterpoint that three-fold, qualitative distinction against the four broad types of love indicated in his title.

Lewis states that just as Lucifer (a former archangel) perverted himself by pride and fell into depravity, so too can love – commonly held to be the arch-emotion – become corrupt by presuming itself to be what it is not.

It is described as the most natural, emotive, and widely diffused of loves: It is natural in that it is present without coercion, emotive because it is the result of fondness due to familiarity, and most widely diffused because it pays the least attention to those characteristics deemed "valuable" or worthy of love and, as a result, is able to transcend most discriminating factors.

Affection has the appearance of being "built-in" or "ready made", says Lewis, and as a result, people come to expect it irrespective of their behaviour and its natural consequences.

[12] Our species does not need friendship in order to reproduce, but to the classical and medieval worlds, it is a higher-level love because it is freely chosen.

He notes that he cannot remember any poem that celebrated true friendship like that between David and Jonathan, Orestes and Pylades, Roland and Oliver, Amis and Amiles.

[18] While accepting that Eros can be an extremely profound experience, he does not overlook the dark way in which it could lead even to the point of suicide pacts or murder, as well as to furious refusals to part, "mercilessly chaining together two mutual tormentors, each raw all over with the poison of hate-in-love".