"To tell of  Your loving-kindness in the morning and Your faithfulness at night" (Tehilim 92:3). Night and day, from a Jewish perspective, are much more than astronomical phenomena. Morning represents hope, confidence, and song. Night represents fear, uncertainty, and loneliness. It is not by chance that Abraham, who ushered in a new way of thinking, is credited with the establishment ofshacharit, the morning prayer; whereas Yaakov, who is identified with exile, instituted ma'ariv, the evening prayer. It is not for naught that Elie Wiesel named his painful and powerful memoir Night.

Apparently, even the superfluous mention of the word "night" is something to be avoided. "Or le'arba asar, on the night of the 14th, we check for chametz" (Pesachim 2a). The Mishnah--instead of using the word laiyla, the actual Hebrew word for night--uses what in this context is the confusing word or. This ambiguity leads to a long Talmudic discussion as to whether the word or might actually mean "night", with source after source quoted demonstrating that the word or is often used as a reference to night in rabbinic literature. Yet one need only read the first few verses of Genesis to realize that the word or means light. "Vayomer Elokim yehi or, vayhei or and G-d said, 'Let there be light', and there was light".

If or means "light"--and it does--then why, the Gemara queries, would the Mishnah use that word to mean "night"? The answer is rather startling. "Rabbi Yehoshua ben Levi said: 'one should never have a distasteful thing emanate from one's mouth'". Thus, for example, the Torah uses the phrase "the animal that is not pure", as opposed to the more direct phrase "the animal that is impure", adding eight seemingly unnecessary letters to the Torah text. Apparently, the word "night", with its negative associations, is one to be avoided.

This principle of avoiding words with negative conations conflicts with a second linguistic rule: "Rav Huna said in the name of Rav in the name of Rav Meir, 'a person should always teach his student in the shortest path'" (ibid 3b). 

The Gemara thus limits the insistence on refined speech to cases where no extra verbiage is needed, helping to explain the many instances where the Torah uses direct and concise--even if "less refined"--speech. Normally, the most direct and shortest way of communicating something is best; however, occasional exceptions are made in order to teach the importance of proper refinement in speech. 

With or being both shorter and more refined than laiyla,the Mishnah preferred the use of that word, despite its potential confusion. Apparently, our Sages wanted to link Pesach with the notion of light.

The Biblical story of Pesach begins with the mitzvah to sanctify the moon when its light is first visible; the holiday itself is celebrated on the 15th of the month when the moon is full; and Pesach is the holiday of hope, confidence, and song. Or, "light", is thus the most appropriate way to begin the tractate--even if in this context, it means night.

The Talmud goes so far as to (correctly) predict that one of the Sages--there is a dispute as to whether it was Rav Yochanan ben Zachai or Rav Yochanan--would become a teacher in Israel just because he stated that one need not squeeze olives in purity, whereas his colleague had stated that one may squeeze olives in impurity. The Talmud understood that leaders can be undone by the slightest slip in their speech--even if what they said was true.

Pesach is the holiday where we are to speak, and teach, and teach some more. Often, more important than whatwe say is how we go about saying it.