The phrase “heaven knows” is an English idiom meaning “no one knows” or “truthfully.” People often say it in response to questions or to reinforce an argument. Many musicians have borrowed the idiom as a title for an album and song.
Perhaps the most common use of this idiom is to claim that no one knows something. For example, in the animated film, “Finding Nemo,” the title character tells his new friend Dory, “Heaven knows what you’re saying!” In other words, Nemo did not understand her and didn’t believe anyone else would be able to either.
The expression often gets extended slightly into the saying “heaven only knows.” This version emphasizes the thought that no one understands except for God. It can be a good response to questions such as “when will this meeting end?” or “where is he?”
People use this idiom to insist that a statement is true. In the 1999 film “Wild Wild West,” villain Dr. Arliss Loveless declares, “We may have lost the war, but heaven knows we haven’t lost our sense of humor.” A character in the classic 1950 move “All About Eve” states vengefully, “Heaven knows she had one coming.” Both speakers use the saying to reinforce the truth of what they say. A less colorful substitute would be the word “really.”
The expression can also be used to say that something is true, even though no one else knows it. A frequent form is the protest, “Heaven knows I tried.” In other words, the speaker knows his opinion may be unpopular or unproven, but believes his statement is still true. Nineteenth century author Charles Dickens writes in Great Expectations, “Heaven knows we need never be ashamed of our tears, for they are the rain upon the blinding dust of earth, overlying our hard hearts.”
Sometimes the word "God" is used in place of "heaven" in this idiom. “God knows” and “goodness knows” are slightly different ways of expressing exactly the same thought. Although some speakers literally mean that God knows, some use the phrase to mean no one else knows. Still others may say this expression sarcastically, implying that there is no God and no one understands at all.
Many artists have borrowed this idiom for songs, albums, and movies. American blues singer Taylor Hicks recorded a single by that title in 2007. In 1957, Robert Mitchum and Deborah Kerr starred as a Marine and a nun in a World War II film called “Heaven Knows, Mr. Allison.”