3 Types of Friendships According to St. Aelred of Rievaulx
Let us allow that, because of some similarity in feelings, those friendships which are not true, be, nevertheless, called friendships, provided, however, they are judiciously distinguished from that friendship which is spiritual and therefore true. Hence let one kind of friendship be called carnal, another worldly, and another spiritual. The carnal springs from mutual harmony in vice; the worldly is enkindled by the hope of gain; and the spiritual is cemented by similarity of life, morals, and pursuits among the just.
(1) CARNAL FRIENDSHIP
Real beginning proceeds from an affection which like a harlot directs its step after every passerby, following its own lustful ears and eyes in every direction. By means of the avenues of these senses it brings into the mind itself images of beautiful bodies or voluptuous objects. To enjoy these as he pleases the carnal man thinks is blessedness, but to enjoy them without an associate he considers less delightful.
Then by gesture, nod, words, compliance, spirit is captivated by spirit, and one is inflamed by the other, and they are kindled to form a sinful bond, so that, after they have entered upon such a deplorable pact, the one will do or suffer any crime or sacrilege whatsoever for the sake of the other. They consider nothing sweeter than this type of friendship, they judge nothing more equable, believing community of like and dislikes to be imposed upon them by the laws of friendship. And so, this sort of friendship is undertaken without deliberation, is tested by no act of judgment, is in no wise governed by reason; but through the violence of affection is carried away through diverse paths, observing no limit, caring naught for uprightness, foreseeing neither gains nor losses, but advancing toward everything heedlessly, indiscriminately, lightly and immoderately. For that reason, goaded on, as if by furies, it is consumed by its own self, or is dissolved with the same levity with which it was originally fashioned.
(2) WORLDLY FRIENDSHIP
Born of a desire for temporal advantage of possessions, is always full of deceit and intrigue; it contains noching certain, nothing constant, nothing secure; for, to be sure, it ever changes with fortune and follows the purse. Hence it is written: "He is a fair-weather friend, and he will not abide in the day of your trouble."? Take away his hope of profit, and immediately he will cease to be a friend. This type of friendship the following lines very aptly deride: A friend, not of the man, but of his purse is he. Held fast by fortune fair, by evil made to flee. And yet, the beginning of this vicious friendship leads many individuals to a certain degree of true friendship: those, namely, who at first enter into a compact of friendship in the hope of common profit while they cherish in themselves faith in baneful riches, and who, in so far as human affairs are concerned, reach an acme of pleasing mutual agreement. But a friendship ought in no wise be called true which is begun and preserved for the sake of some temporal advantage.
(3) SPIRITUAL FRIENDSHIP
Which we call true, should be desired, not for consideration of any worldly advantage or for any extrinsic cause, but from the dignity of its own nature and the feelings of the human heart, so that its fruition and reward is nothing other than itself. Whence the Lord in the Gospel says: "I have appointed you that you should go, and should bring forth fruit," that is, that you should love one another. For true friendship advances by perfecting itself, and the fruit is derived from feeling the sweetness of that perfection. And so spiritual friendship among the just is born of a similarity in life, morals, and pursuits, that is, it is a mutual conformity in matters human and divine united with benevolence and charity.
Taken from Spiritual Friendship, Book 1, Origin of Spiritual Friendships, 38-46