Although the definite origin of this phrase in unknown, yet it seems a likely derivation from some natural phenomenon. There are some fanciful and proposed derivations. It was Jonathan Swift, who first used it in his satirical poem, “A Description of a City Shower” in 1710. Later, he used it again in his book, “A Complete Collection of Polite and Ingenious Conversation” in 1738. It reads as, “Nay, I know Sir John will go, though he was sure it would rain Cats and Dogs. But, pray stay, Sir John, you’ll be Time enough to go to Bed by candle-light.” Its literal meaning is raining heavily, and it refers to poor sanitary conditions in London. Metaphorically, Swift denounces the contemporary London society for living in such conditions.
In fact, Swift alluded to the filthy streets of England in the early eighteenth century, when heavy rains would carry along with debris and dead animals. Swift shows another meanings how people make connections in trying to avoid storm. Nevertheless, when it is over, they return to their own ways separately. He simply means that sometimes we need to forget and set aside our differences and treat one another as equals, not enemies.
At that time, it was used only in terms of rain. For instance, if a flood or hurricane comes in our neighboring country, we all would likely to get together with our neighbors. But when hurricane is over, majority of the people would not even speak to their neighbors after that. This is exactly the message Swift has tried to convey. However, now it is used only for heavy rains, storms and hails.
This phrase is taken from Jonathan Swift’s book “A Complete Collection of Polite and Ingenious Conversation” where Lord Sp speaks it as;
“Nay, I know Sir John will go, though he was sure it would rain Cats and Dogs. But, pray stay, Sir John, you’ll be Time enough to go to Bed by candle-light.”
Swift used this line as a satirical commentary on upper classes in England. Metaphorically, the author has referred to the behavior of the people during change in weather conditions. At the end of the 17th century, large cities around the world fought poor sanitary conditions due to overcrowding or shortage of sewers and plumbing. Therefore, there were bouts of dysentery and plagues.
Swift has alluded to the filthy streets of England in early 18th century, when heavy rains would carry along debris and dead animals. The animals had not fallen from the sky; rather, the sight of these dead animals floating by in rains and storms could have been the cause of coining of this phrase. It satirically examines the behavioral changes of people during a crisis or a storm. Rain is an unfortunate condition; however, it brings people together. He also points to the fact that people from all social classes come together whenever they need to, regardless of the value of their social status. When world is burning down, who cares about social class if all are dying? Hence, Swift explains it by talking about drowning of cats and dogs alike.