ELECTIVE AFFINITIES

Those natures which, when they meet, quickly lay hold on and mutually affect one another we call affined. This affinity is sufficiently striking in the case of alkalis and acids which, although they are mutually antithetical, and perhaps precisely because they are so, must decidedly seek and embrace one another, modify one another, and together form a new substance.

- The Captain in Goethe's Die Wahlverwandtschaften