It is universally held that the unicorn is a supernatural being and of auspicious omen; so say the odes, the annals, the biographies of worthies, and other texts whose authority is unimpeachable. Even village women and children know that the unicorn is a lucky sign. But this animal does not figure among the barnyard animals, it is not always easy to come across, it does not lend itself to zoological classification. Nor is it like the horse or bull, the wolf or deer. In such circumstances we may be face to face with a unicorn and not know for sure that we are. We know that a certain animal with a mane is a horse and that a certain animal with horns is a bull. We do not know what the unicorn looks like.

Book of Imaginary Beings (1957), as translated by Norman Thomas di Giovanni