Between is used when there are only two elements involved. For example: This is between him and her; we should stay out of it.
Usage expands to cover collective things: The disagreement between managers and workers is serious.
Among is used when there are more than two things. We discussed the issue among the three of us. Or, We must choose from among A, B, or C.
According to a widely repeated but unjustified tradition, "between is used for two, and among for more than two." It is true that between is the only choice when exactly two entities are specified: the choice between (not among) good and evil, the rivalry between (not among) Great Britain and France. When more than two entities are involved, however, or when the number of entities is unspecified, the choice of one or the other word depends on the intended sense.
Between is used when the entities are considered as distinct individuals; among, when they are considered as a mass or collectivity. Thus in the sentence The bomb landed between the houses, the houses are seen as points that define the boundaries of the area of impact (so that we presume that none of the individual houses was hit). In The bomb landed among the houses, the area of impact is considered to be the general location of the houses, taken together (in which case it is left open whether any houses were hit).
By the same token, we may speak of a series of wars between the Greek cities, which suggests that each city was an independent participant in the hostilities, or of a series of wars among the Greek cities, which allows for the possibility that the participants were shifting alliances of cities. For this reason, among is used to indicate inclusion in a group: She is among the best of our young sculptors. There is a spy among you. Use between when the entities are seen as determining the limits or endpoints of a range: They searched the area between the river, the farmhouse, and the woods. The truck driver had obviously been drinking between stops.
Usage Discussion of BETWEEN
There is a persistent but unfounded notion that between can be used only of two items and that among must be used for more than two. Between has been used of more than two since Old English; it is especially appropriate to denote a one-to-one relationship, regardless of the number of items. It can be used when the number is unspecified <economic cooperation between nations>, when more than two are enumerated <between you and me and the lamppost> <partitioned between Austria, Prussia, and Russia — Nathaniel Benchley>, and even when only one item is mentioned (but repetition is implied) <pausing between every sentence to rap the floor — George Eliot>. Among is more appropriate where the emphasis is on distribution rather than individual relationships <discontent among the peasants>. When among is automatically chosen for more than two, English idiom may be strained <a worthy book that nevertheless falls among many stools — John Simon> <the author alternates among modern slang, clichés and quotes from literary giants — A. H. Johnston>.