In his famous little book, CS Lewis differentiated the "four" loves as affection, friendship, eros and agape . The terms are all derived from Greek roots, but Lewis kept the Greek in the last two because the words have become so familiar, they hardly seem foreign any more.

The four loves are not distinct or separable loves. As we know from experience, connections and inter-relations exist between them. Lewis wrote to show that the first three loves are never properly themselves unless they respect the priority of the fourth. "Love," he writes, "begins to be demon the moment it begins to be a god." That is, the moment it usurps the role of God or becomes identified with God. While "God is love," as St John tells us, the converse does not follow, that "love is God."

Affection refers first perhaps to the love between parents and children, and vice versa, though it is not limited to this. It is the least discriminating of all the loves. Almost anyone can become the object of affection, the ugly, the stupid, the exasperating, the slow. One sees it between a brother and a sister with Down Syndrome, or between a nuclear physicist and a maid.

Affection has its own criteria, and the most pertinent of these is familiarity. The objects of affection must be familiar. One can often remember the day - or the hour - when eros struck, but to be aware of affection is to be aware that it had been going on for some time.

A dog will wag its tail at someone who usually mistreats it and bark at someone desperately trying to be a friend. A little child will act the same way. The key is familiarity.

Affection is the humblest of the loves. It is essentially modest and without airs. It would cease to be itself if it were loudly and frequently expressed. Eros must keep talking and proclaiming its ardour; affection conveys itself with a smile and a shrug.

Affection can enter into the other loves, colour them, and become the medium through which they express themselves. Friendship and affection are different loves, but an old friend is not just a friend.

An old friend elicits affection in ways a newly made friend cannot. Things that have nothing to do with the friendship become dear and familiar for being associated with an old friend over time.

At one time, the interrelatedness of the loves had a common expression in the kiss. Friendship no longer employs it, save in Latin countries, but affection and eros still do. A kiss out of eros , of course, is not the same as a kiss out of affection, but "not all kisses between lovers are lovers' kisses."

Both affection and eros also use "baby talk" to express intimacy and tenderness. Zoologists have shown that this is not peculiar to the human species. Mummy chimps squeeze baby chimps and fall into baby chimp language. Among humans, baby talk is the earliest form of tenderness recalled to do duty for more adult forms.

Unlike friendship, affection is not the result of choice. We choose our friends and lovers. We sometimes say of such choices things like "they are made for each other." Affection unites people who decidedly are not made for each other, who, if fate had not thrown them together in some way, would have had nothing to do with one another.

The person is treated with affection just because they are there . After a while, one notices that there is something about them. He or she, we say, is a good person " in their own way ." What's happening is that we are beginning to appreciate goodness in itself, not only as it suits us or pleases us. We discover the beauty of affection with appreciation.

All the loves have their downsides, and affection is no exception. Like agape , it can love the unlovely, but it can also be the cause of great unhappiness. Within families, for instance it can make or impose insatiable demands.

A parent is excessively "caring," always there "waiting up," even if the furthest you go is next door. Affection can need to be needed in a suffocating way, reluctant to concede that certain forms of love must work towards their own abdication.

Affection can also be as fiercely jealous as erotic love. All the loves are liable to jealously, but affection as the most natural can also be the fiercest. This arises from its close association with the old and the familiar. A brother or a sister, for instance, can grow up sharing everything, till one of them streaks ahead.

A new interest is discovered - poetry or science, or one of them undergoes a religious conversion. The other is left behind. A more miserable sense of desertion can hardly be imagined.

Affection can thus be a very needy love, which learns to let go only with a great deal of pain. It, too, becomes deeper only as it enters into life's paschal dimension. The way to renewal and depth - the way to life - is through freely embraced forms of death.