When speaking about the ritual of searching for hametz on the night before the first seder, the 14th day of the Hebrew month Nisan, the first Mishnah of the Tractate of Pesahim plays with imagery of light:
“Light of the fourteenth—we search for leaven with the light of a candle.”
".אור לארבעה השר בודקים את החמץ לאור הנר"
The word light is used twice in one short sentence, yet does not mean the same thing in both instances. Indeed, the Gemara tells us that the two uses reflect opposite meanings. As the Rabbis of the Talmud understand it, “light of the fourteenth” does not refer to the literal meaning of these words.
Instead, light refers not to the light of day, but the darkness of evening. Consequently, the Mishnah is teaching us that the ritual of the search for hametz should be performed in the darkness of the night before Passover. The second use of the term light, however, does in fact refer to light, as the Mishnah instructs us to search for hametz by the light of a candle.
Of course, this presents us with the obvious question: Why did the Rabbis use the word light when they intended darkness? The Hebrew word leila (לילה) would certainly have worked. Why did the Rabbis not say what they meant?
Maimonides, in his commentary to the Mishnah, suggests a compelling explanation for this unusual use of the word light: he suggests the Rabbis were guided by literary concerns. That is to say, it would have been less aesthetically pleasing to begin the tractate on the holiday of Passover with the word night. Darkness intimates an absence, while light (illumination) allows for the appreciation of abundance.
Truth be told, using a word that is the opposite of what one intends is not unknown in both biblical and rabbinic Hebrew. When Jezebel plants false witnesses against Naboth, she tells them to accuse Naboth of having “reviled God and king.” The word used in I Kings 21:10 for reviled is beirakhta (blessed)—the opposite of what the intended meaning is.