Q: How did the expression “double-edged sword” come to mean something that has both positive and negative results?
A: The expression ultimately comes from the use of “two-edged sword” in Hebrew, Greek, and Latin versions of the Bible to mean something very sharp, like a weapon or piercing words.
Here are a few examples we’ve found for “two-edged sword” in Hebrew (חרב פיפיות), Greek (μαχαιρας διστομου), and Latin (gladio ancipiti) from the Old and New Testaments:
• “רוממות אל בגרונם וחרב פיפיות בידם” (“Praise of God in their mouths and a two-edged sword in their hand”). From the 10th-century Aleppo Codex of the Hebrew Bible, Psalms 149:6 (thought to have originated around 1000 BCE).
• “υστερον μεντοι πικροτερον χολης ευρησεις και ηκονημενον μαλλον μαχαιρας διστομου” (“Later however you will find her [an immoral woman] more bitter than gall and sharper than a two-edged sword”). From the Septuagint, Proverbs 5:4, believed translated in the second century BCE.
• “vivus est enim Dei sermo et efficax et penetrabilior omni gladio ancipiti” (“for the word of God is living and powerful and more penetrating than any two-edged sword”). From the Vulgate, Epistle to the Hebrews 4:12, dating from the late fourth and early fifth centuries of the Common Era.
(The medieval Jewish scholar Rashi [1040-1105] interprets Psalm 149:6 figuratively in the first example above: “With paeans to God in their throats, and these same are like two-edged swords in their hands.” Rashi’s Commentary on the Psalms, 2004, translated by Mayer I. Gruber.)
Why is the expression “two-edged sword” used in the Bible to describe the word of God? Perhaps because the Hebrew noun for “edge” here, פה, can also mean “mouth,” among other things.
The plural of פה is פיות (“edges” or “mouths”) and the construct state, or genitive, is פיפיות (“of edges” or “of mouths”). So חרב פיפיות (“a sword of edges,” usually translated as “two-edged sword”) could also mean “a sword of mouths”—that is, a source of sharp words.
Similarly, when the phrase “two-edged sword” first appeared in English, it was used to describe the word of God. The Oxford English Dictionary’s earliest example, which we’ve expanded, is from Hebrews 4:12 in William Tyndale’s 1526 translation of the New Testament:
“For the worde of god is quycke and myghty in operacion and sharper then eny two edged swearde.”
As far as we can tell, the sense of “two-edged sword” as something with both good and bad consequences appeared a few decades later.
The earliest example we’ve found is from an English translation of a Latin sermon about the Apocalypse by the Swiss pastor, reformer, and theologian Heinrich Bullinger (1504-75):
“For a sharpe two edged sworde commeth out of the Lordes mouth. This swearde is the worde of God … And it is two edged, sharpe and pearsing, as well as in the heart of the Godly unto saluation, as well as in the heartes of the wycked to payne and condemnation.” (From A Hundred Sermons Vpo[n] the Apocalips of Iesu Christe, 1561, John Daus’s translation of Bullinger’s sermons.)
Getting back to “double-edged sword,” the usual wording now, the expression is used literally for an actual weapon in the earliest example we’ve found:
“And in their mouths let be the actes of God the mighty Lord / And in their hands let them beare a double edged sword” (Psalms 149:6, The Whole Books of Psalmes, 1581, by Thomas Sternhold, John Hopkins, and others).
The first example we’ve found with the phrase used figuratively in its good-bad sense is from a sermon that says the Gospel has both “the power of God to salvation” and “the power of God to confusion”:
“It is a double-edged Sword, and giues, vel vitam, vel vinditam, either instruction, or destruction” (from A Divine Herball Together With a Forrest of Thornes in Five Sermons, 1616, by the English clergyman Thomas Adams).
As for the ultimate origin of the “good/bad” sense of “double-edged sword,” Dictionary.com suggests that it “seems to be based on an idea that a sword with two edges poses a danger of bouncing back and cutting its own wielder.” However, we’ve seen no evidence to support this idea.
We’ve also seen no evidence that the English expression is ultimately derived from the Arabic term for a two-edged sword, سلاح ذو حدين, as suggested by the collaborative dictionary Wiktionary.