The First Drops of the Phrase

The earliest recorded appearance of a phrase similar to 'raining cats and dogs' dates back to 1651. British poet Henry Vaughan, in his collection Olor Iscanus, wrote of a roof robust enough to withstand “dogs and cats rained in shower”. A year later, English playwright Richard Brome used a variant in his comedy The City Wit, where he penned the line, “It shall rain dogs and polecats” — referring to polecats, which were common in Britain at the time.

Swift's Storm of Popularity

While these early mentions exist, it was the renowned Irish satirist Jonathan Swift who is largely credited with propelling the idiom into widespread use. In his 1738 satire, Complete Collection of Genteel and Ingenious Conversation, a character expresses fear that it might “rain cats and dogs”. Swift had also, in 1710, penned the poem City Shower, which vividly described the aftermath of heavy floods in London, featuring dead animals littering the streets. This imagery may have deeply influenced the popular understanding and adoption of the phrase.

Mythical Menagerie and Linguistic Leads

Several theories attempt to explain why cats and dogs specifically became associated with torrential rain. One theory points to Norse mythology, where Odin, the god of storms, was often depicted with dogs and wolves representing winds, and witches were believed to ride brooms with black cats during storms, symbolizing heavy rain for sailors. Another linguistic hypothesis suggests the phrase might be a corruption of the obsolete English word 'catadupe,' meaning a waterfall or cataract, derived from ancient Greek.

The Grim Reality of a Downpour

Perhaps the most grounded, though less romantic, theory suggests the phrase stems from the deplorable street conditions of 17th and 18th century cities. Poor drainage meant that during heavy rains, streets would flood, sweeping away debris and unfortunately, the carcasses of dead animals like cats and dogs. The sight of these animals being carried along by the deluge could have led people to describe the extreme weather as literally 'raining cats and dogs.'

Debunking the Thatched Roof Myth

A popular misconception holds that cats and dogs would seek shelter in thatched roofs and then be washed out during heavy storms. However, this theory is largely considered apocryphal. Well-maintained thatched roofs are designed to be quite waterproof and sloped, making it unlikely for animals to reside on their exterior surfaces or be easily dislodged by rain.