Pledge and Promise have the same meaning if both words are used as noun. As verbs the difference between promise and pledge is that promise is to commit to something or action; to make an oath; make a vow while pledge is to make a solemn promise (to do something). As nouns the difference between pledge and donation is that pledge is a solemn promise to do something while donation is a voluntary gift or contribution for a specific cause.

As nouns the difference between pledge and oath is that pledge is a solemn promise to do something while oath is a solemn pledge or promise to a god, king, or another person, to attest to the truth of a statement or contract. As nouns the difference between vow and pledge is that vow is a solemn promise to perform some act, or behave in a specified manner, especially a promise to live and act in accordance with the rules of a religious order while pledge is a solemn promise to do something. Promise means that I commit do something, not necessarily any payment.
As nouns the difference between promise and pledge is that promise is an oath or affirmation; a vow while pledge is a solemn promise to do something. As verbs the difference between oath and promise is that oath is (archaic) to pledge while promise is to commit to something or action; to make an oath; make a vow. There slight difference is if both words are used as verbs.

A pledge is a promise to pay something. Pledge is to guarantee by a solemn promise or word of honor and assume that obligation. Examples: I promise to write you once a week. I pledge allegiance to the flag (I promise to pay respect and give of my time and service.) We can consider the following basis of comparisons between both bailment and pledge. Let us now study the head to head differences between bailment and pledge. As verbs the difference between pledge and oath is that pledge is to make a solemn promise (to do something) while oath is (archaic) to pledge. As a verb pledge is to make a solemn promise (to do something). Promise as verb means give word that something will be done or to be done. 1) Meaning and Definition: A bailment refers to a transfer of movable goods from one party to another party for any specific purposes such as service, promise or need. As nouns the difference between oath and promise is that oath is a solemn pledge or promise to a god, king, or another person, to attest to the truth of a statement or contract while promise is an oath or affirmation; a vow. Examples: I pledged $100 to the charity this year.