Raining cats and dogs

Raining cats and dogs means very heavy rain but why cats and dogs? We know that its first appearance, in a slightly modified form, is in 1653 in Richard Brome’s The City Wit, “It shall raine … dogs and polecats.” Why dogs and ‘polecats’ is not known. In olden days, drowned cats and dogs were frequently seen in gutters and storm drains after severe storms. Such observations may have prompted Jonathan Swift to pen the first known citation of the idiom, as we know it today, when he wrote in 1738, “I know Sir John will go, though he was sure it would rain cats and dogs.” This seems to be the most plausible origin of the idiom. Firstly, an expression of dubious meaning that first surfaces in the mid-16th century, followed up by frequent observations of drowned cats and dogs, and then use of the phrase, as we now know it, from Jonathan Swift. Most other explanations of its origin, for example, cats and dogs living in the thatch of houses and then sliding off in the rain, are apocryphal.