For the source text click/tap here: Shavuot 26
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What if one only thinks the oath? Is it necessary to speak the oath aloud be liable if the oath is broken? A baraita notes that an oath is not in the heart alone. If a person resolved in his heart to say an oath but never spoke it aloud, some rabbis say that he is not liable. However, the rabbis determine that an oath must be spoken.
Which leads us to the thorny issue of lip service from the semantic and metaphoric perspective.