Oath, pledge, and vow: What is the difference between these words and where should I use each word? A simple example would help me to understand.
To me, the nouns pledge and vow are closer in meaning, to the point of being synonyms. They mean “a solemn promise” (this is NOAD's main definition for both). Oath, while close in meaning, typically has an additional sense of invoking the divine (e.g., an oath taken on the bible). A verb with close meaning to all three is to swear.
In addition to this meaning of “solemn promise”, each of these three nouns has specific additional meanings.