Key Difference: Promise is an assurance or declaration of doing something or related to happening of something. Commitment refers the declaration for which one tends to becomes dedicated to ensure that the declaration holds true.

Most of the people get confuse with the terms like promise and commitment, and the confusion is regarding that when they should refer a declaration as promise and when it should be considered as a commitment. There is a close relation between them, but still the minor difference between them is still able to distinguish them. Sometimes, promise is judged as a commitment if the dedication is involved in the promise, and this interpretation is not wrong. Thus, many times they can also be used interchangeably.

‘Promises’ is a word of common usage. We make promises and many promises are made to us. Oxford Dictionary defines promise as ‘a declaration or assurance that one will do something or that a particular thing will happen’. We promise in order to declare or assure someone (an individual or group); this insurance can be for the act of doing something or regarding the happening of a particular thing. Let us consider some examples- ‘I promise that one day, my parents will be proud of me’. This statement can be taken as a declarative statement, indicating that he will do something or become something that will make his parents proud. ’I promise to study very hard from today’; in this statement the person is assuring that he will study hard. All these examples are referring to some acts that are declared to be done.

Oxford Dictionary defines commitment as ‘the state or quality of being dedicated to a cause, activity, etc.’ Dedicated means devoted to the concerned thing. Dedication 

comes  from actions; one must fully devote and therefore act to achieve the results.” He is a dedicated social worker”, is referring a person who has devoted himself to the work of social reforms as a social worker. Dedication means that he considers this task as his priority and he is also honest about his work. The commitment involves the actions that are performed to fulfill  the promises. "My commitment is to complete the work on time", in this sentence one can associate the word devotion with which the person intends to complete the work.

To understand the relationship between a promise and a commitment, we can just define the difference by saying that promises come true by the involvement of commitment. A person may promise just for the sake of it, and may be after making a promise forgets about it, then somewhere commitment is lacking. Therefore, commitment is suitable for those who want to make a declaration but with all the elements of dedication. A promise may or may not hold true in the future, but the commitments are more likely to be met.