Question What is the origin of the phrase "it's raining cats and dogs?"

Answer

We don’t know. The phrase might have its roots in Norse mythology, medieval superstitions, the obsolete word catadupe (waterfall), or dead animals in the streets of Britain being picked up by storm waters.

Very unpleasant weather. George Cruikshank, 1820. Ailsa Mellon Bruce Fund, National Gallery of Art

The first recorded use of a phrase similar to “raining cats and dogs” was in the 1651 collection of poems Olor Iscanus. British poet Henry Vaughan referred to a roof that was secure against “dogs and cats rained in shower.” One year later, Richard Brome, an English playwright, wrote in his comedy City Witt, “It shall rain dogs and polecats.” (Polecats are related to the weasel and were common in Great Britain through the end of the nineteenth century.)

In 1738, Jonathan Swift published his “Complete Collection of Genteel and Ingenious Conversation,” a satire on the conversations of the upper classes. One of his characters fears that it will “rain cats and dogs.” Whether Swift coined the phrase or was using a cliché, his satire was likely the beginning of the phrase’s popularity. Other British writers have employed less popular phrases, such as “it’s raining pitchforks” or “it’s raining stair-rods,” to describe the shaft-like appearance of heavy rains. But Swift’s phrase may have been memorable enough to stick in the mind of the public.

Swift also wrote a poem, “City Shower” (1710), that described floods that occurred after heavy rains. The floods left dead animals in the streets, and may have led locals to describe the weather as “raining cats and dogs.”

Honorable Mr. Cat. Helen Hyde, 1903. Prints & Photographs Division, Library of Congress

Why “cats and dogs”?

Again, we don’t know for certain. Etymologists—people who study the origins of words—have suggested a variety of mythological and literal explanations for why people say “it’s raining cats and dogs” to describe a heavy downpour. Here are some of the popular theories: