elective affinity

Has the naturalist or chemist learned his craft, who has explored the gravity of atoms and the elective affinities, who has not yet discerned the deeper law whereof this is only a partial or approximate statement, namely, that like draws to like; and that the goods which belong to you, gravitate to you, and need not be pursued with pains and cost?

Matrimony was not a matter of elective affinity between two persons seeking to spend their lives agreeably and profitably in common, so much as an institution used by the state for raising vigorous recruits for the national army.

Weber spoke of an elective affinity between a form of religious belief (Protestantism) and a practical ethics (the work ethic of capitalism). His idea can be extended to explain how different groups come to have a basis for entering a single party.