Friendship
Friendship is not thought of a love by moderns. One obvious reason is that very few people have experienced try friendship. It is possible to live without friendship. Friendship has nothing to do with love-affair. It is not limited to 2 people; in fact it is better if there are more.
It is not companionship, important for the community in its own way. Although companionship can lead to friendship. Friendship arises when two people realize they care about the same thing, be it their view of God or white mice.
It can be beneficial to the community; it can also be a detriment.
There is not duty involved. There are no claims of implications of necessity.
Lewis discusses friendship between the sexes and gets a bit sexist for my taste.
Friendship circles have some inherent possible problems. By nature they are exclusive and hence can easily become prideful. They are also by nature a secession, even a rebellion from common practice. As a result, then can become haughty and turn a deaf ear to other voices. "the mass of the people, who are never quite right, are never quite wrong."