Themes & Theology of Speech
Speech is action. Long before 20th-century analytic philosophers, Jewish sages emphasized that speech is not "mere words" but concrete reality. They noted that in some cases, "one who speaks of a deed [incurs punishment] more severe than one who actually committed it" (Mishnah Arakhin 3:4). The proof that saying is doing comes from the divine realm: "Speech is like action--from where do we learn this? Scripture teaches, 'By the word of the Lord the heavens were made' (Psalms 33:7)" (Babylonian Talmud, Shabbat 119b).
Therefore the wisdom teachers of Talmudic Judaism urged caution in speech. "Judge your words before letting them emerge from your mouth," urges the minor tractate Derekh Eretz Zuta (Chapter 3). Thus one may avoid the many pitfalls of speech.
Among those damaging forms of speech is vulgarity. A midrash on Deuteronomy 23:5 examines the warning "Let your camp be holy; Let Him not see among you anything unseemly… lest He turn away from you…" The phrase the Torah uses for "unseemly" is ervat davar, which literally means "a shameful/naked thing." The midrash asks what that "ervat davar" might be. The reply: "It is an ervah in dibbur"--a shameful thing in speech--and explains, "This means vulgar speech" (Leviticus Rabba 25).
Speech has more levels of appropriateness that just "acceptable" and "vulgar." Some levels are higher than the quotidian norm. "Let not your Shabbat speech be like your daily speech," the Talmud adjures (Babylonian Talmud, Shabbat 113b). Appropriate speech is part of the experience of higher spirituality that the Sabbath should provide.
Another reason for caution is that despite its ephemeral medium, speech, once heard, is permanent and irreversible. Precipitous speech can ensnare us in unwise and unwanted obligations. Talmudic sages railed against failure to live up to one's verbal commitments. "One who retracts his speech--the Sages are unhappy with him" (Tosefta Bava Metzia, Chapter 3).