if someone tells you not to look a gift horse in the mouth, what they’re suggesting to you is that you shouldn’t criticize or question something good being offered to you with no strings attached.
Throughout recorded history, the horse has been a prized possession of man. The horse has plowed fields, hauled goods, pulled carriages, carried riders and more. Back in the day when horses were bought and sold, it was good business practices to check the age and health of a horse by examining its lower jaw and its teeth. A horse’s history could be told by what one found in its mouth. That being said, it was also considered the height of bad manners to examine a horse’s mouth when the horse was being given as a gift.
Even back on December 5, 1926 the New York Times ran a story entitled, “Those Who Take Casual Gifts May Fina A String Attached” that read:
Never look a gift horse in the mouth is a saying that has become largely obsolete with the diminishing ranks of horses in New York. Yet the danger persists: and it is as true today as it was true yesterday that gifts do not invariably fall out of a clear sky in this metropolis
That was all fine and dandy but on June 28, 1854 the same newspaper published a news article entitled, “Naval Rules And Regulations.” It read in part:
Never look a gift horse in the mouth. Chesterfield says, never quote a proverb; but “French On The Lessons In Proverbs,” a more recent and learned authority, and also dispute the proverb. It had been much better for those old Trojans if they had looked their gift horse in the mouth; and since that memorable example of gift-bearing treachery, one has often reason to exclaim, “Timco Danaos et dona ferentes. The free gift Manual looks very much like an attempt to steal into the service, once again, obsolete and repudiated rules, which never could be introduced in an open, frank and legal manner.
With regards to the book, The Works of Charles and Mary Lamb: Miscellaneous Prose, 1798-1833, The Athenceum of February 16, 1833 reviewed the book and is quoted as saying:
Here is a portrait of Mrs. Conrady. We agree with the writer that ‘ no one that has looked on her can pretend to forget the lady.’ The point ought to be cleared up. That we must not look a Gift horse in the mouth.
Now John Heywood (1497-1580) wrote the following in his book, “A Dialogue of the Effectual Proverbs.”
Where gifts be given freely — east, west, north or south —
No man ought to look a given horse in the mouth.
And though her mouth be foul she hath a fair tail —
I consider this text, as is most my avail.
In want of white teeth and yellow hairs to behold,
She flourisheth in white silver and yellow gold.
What though she be toothless, and bald as a coot?
Her substance is shoot anker, whereat I shoot.”
St. Jerome of Stridonium (347 – 420), an Illyrian Catholic priest is believed to have first used the phrase in reply to his literary critics. His exact words: “Never inspect the teeth of a gift horse.”
Historically Speaking 