What is the difference in usage between \"until\" and \"before\" when used as conjunctions?

If time is used as the dividing line, \"until\" emphasizes that an action occurs before a certain moment, while \"before\" emphasizes that the action occurs after that moment.

In negative sentences, until is equivalent to before; until indicates up to what point in time. Before emphasizes that a certain state persisted up until the point of cessation

In fact, as long as we keep in mind the inherent meanings of using these two elements, as well as whether the verb in the main clause is finite or infinite, and whether it is in the affirmative or negative form, we can easily resolve such problems. The details are explained as follows: First, in the following situations, the two can be used interchangeably, but their meanings differ slightly. Before means “prior to …”, emphasizing the sequence of times ； While “until” means “up to... before”, when the main clause is a positive sentence, it indicates the time at which the action in the main clause comes to an end ； If the main clause is a negative sentence, it emphasizes the starting time of the action in the main clause. 1. The main clause has a negative terminal predicate verb. Common verbs include open, start, leave, arrive, finish, stop, etc. For example: (1) The noise on the street didn’t stop until/before midnight. (2) The children won’t come back until/before it gets dark. (3) I didn’t leave the lovely boy until/before his mother came home. 2. When the main clause is in the affirmative form and involves a continuous verb, verbs such as stand, stay, talk, be, wait, etc., are used. For example: (1) He lived with his parents until/before he graduated from school. (2) I will wait until/before he comes to my help. (3) I shall stay here until/before you come back. II. In the following situations, use before instead of until. 1. For the affirmative, finite predicate verb in the main clause, only before is used. Examples: (1) He fell asleep before I could take off his clothes. (2) We arrived there before it started to rain. (3) The holiday came to an end before I knew it. (4) He almost knocked me down before he saw me. 2. When the predicate verb in the main sentence is used to emphasize the slowness of an action, only \"before\" is used, and it is often accompanied by time-related adverbs or phrases indicating a time period. Examples: (1) It was quite some time before he found the elephant at all. (2) We had walked a long way before we found some water. (3) We had sailed for two days before we saw the land. (4) The fire lasted about four hours before the firefighters could control it. (5) It was midnight before my brother came home. (6) It was three months before they met again. 3. If what is emphasized is that the action in the subordinate clause did not occur before the action in the main clause took place, then only “before” is used. It is often translated as “before”, “not” or “before …”. Examples: (1) We can leave early in the morning before it gets too hot. (2) I must write it down before I forget it. (3) We do want to buy something now before prices go up. 4. To express “rather than... it’s better to...”, “instead of... it’s preferable to...”, only ‘before’ is used. Examples: (1) I would give up my job before I’d agree to be dismissed. (2) He will die of hunger before he will steal. 5. Before is used in certain specific sentence structures. For example: (1) It was not long before the whole country rose up. (2) It will probably not be long before they understand each other. III. In the following situations, until is generally used to make a distinction. 1. When the main clause contains a continuous predicate verb, both affirmative and negative forms are possible, but their meanings are completely different. The affirmative form indicates the termination of an action, while the negative form indicates its initiation. For example: (1) We discussed the problem until/before he came back. We kept discussing it until he returned. (2)We didn’t discuss the problem until he came back. We waited until he returned before discussing it. 2. Although the ‘not…until’ structure can be used interchangeably with ‘before’ in some cases, ‘until’ is generally still used in emphasis sentences. For example: (1) It was not until he told me that I knew it. (2) It was not until he finished his homework that he went home.