What is the difference between and oath and a vow?

[Guest Nicole]

What is the difference between and oath and a vow?

[Evacuated]

For starters:

*** Insight-2 p. 1162 Vow ***
VOW
A solemn promise made to God to perform some act, make some offering or gift, enter some service or condition, or abstain from certain things not unlawful in themselves. A vow was a voluntary expression made of one’s own free will. Being a solemn promise, a vow carried the force of an oath or a swearing, and at times the two expressions accompany each other in the Bible. (Nu 30:2; Mt 5:33) “Vow” is more the declaration of intent, while “oath” denotes the appeal made to a higher authority attesting to the truthfulness or binding nature of the declaration. Oaths often accompanied attestation to a covenant.—Ge 26:28; 31:44, 53.
 

[The Librarian]

I thought it might be interesting to see how these words were understood and differentiated by reference works over the past hundred years or so. Unfortunately, the coverage of the three terms in synonym dictionaries is somewhat spotty (though still interesting) across the years. Here is what some authorities have said. From James Fernald, English Synonyms and Antonyms (1896):

In the highest sense, as in a court of justice, "an oath is reverent appeal to God in corroboration of what one says," ABBOTT LAW DICT[IONARY]. ...An oath is made to man in the name of God; a vow, to God without the intervention, often without the knowledge, of man. In the lower sense, an oath may be mere blasphemy or profane swearing.

This book doesn't include pledge in the same group of words with oath and vow, but instead lists it with (among other terms) compact, covenant, obligation, pact, promise, and stipulation, under the general heading contract, remarking

All of these words involve at least two parties, tho an engagement or promise may be the act of but one.

Webster's Dictionary of Synonyms (1942) doesn't cover oath or vow, but offers these comments in distinguishing the verb pledge from the verb promise:

Quote

Promise, engage, pledge, plight, covenant, contract come into comparison as meaning to give one's word that one will do make, give, accept, or the like, something stipulated. Promise,both as a transitive and as an intransitive verb, implies a giving assurance (usually orally or in writing) but it suggests no further grounds for expectation of the fulfillment of what is promised; [examples omitted]. ... Pledge, chiefly a transitive verb may imply either the giving voluntarily of a promise by some actor words that suggest the giving of a solemn assurance, or the provision of a formal guarantee (as to pledge one's honor that one will see that a dying friends wish is respected; [other examples omitted]), or the putting of another or of others under a solemn promise to do, to forbear, or the like [examples omitted].

The noun forms of pledge associated with the verb forms described here would involve the promise or guarantee or security that the specified action will be performed.

S.I. Hayakawa, Choose the Right Word: A Modern Guide to Synonyms (1968) again passes over oath and vow, but addresses pledge as a noun in some detail:

Quote

pledge, bail, bond, collateral, guarantee, security. These words refer to a promise that is backed up in someway and reinforced by the commitment of one's honor or material possessions. Pledge is the most general of these, applying in any case where someone solemnly promises to remain loyal to a principle or to undertake a given task: the Pledge of Allegiance to the Flag; a pledge of $10,000 to the Alumni Fund; a pledge to have the alterations completed by Friday. Only the person's honor backs up his promise in this case.

And finally, Merriam-Webster's Dictionary of Synonyms (1984) examines pledge as a noun in the company of four related nouns:

Quote

Pledge, earnest, token, pawn, hostage are comparable when they denote something that is given or held as a sign of another's faith or intention to do what has been promised. Pledge, originally and still in some applications a technical legal term, applies in general to something handed over to another as a token [example omitted], or as security for the performance of an obligation or payment of a debt [examples omitted].

These discussions suggest that though oath, vow, and pledge are all promises, they have different focuses. An oath is a swearing in the presence of God with regard to a commitment one is making to one or more other people (as to tell the truth as a witness in court, or to uphold the dignity of one's office). A vow is a promise to God (or to something philosophically analogous) to accept and discharge faithfully some specified spiritual or material obligation. A pledge is a promise on one's honor or sense of duty to take some action in fulfillment of a contract with other human beings.

https://english.stackexchange.com/questions/11565/oath-vs-pledge-vs-vow