Discussion of 由不得 [yóu bu de] not be up to somebody; cannot help but... - Trainchinese

1 - 由得 and 不由得 (=由不得) are antonyms. 由得 means “can be up to (someone's decision), can be someone's say“. The opposite of 由得 is 不由得 or 由不得 - not be up to somebody Note that 不由得 and 由不得 have another meaning, which is “cannot help but...“. 不得不 means “have to, have no choice or option but to“ The difference here is that when 不由得 and 由不得 means “cannot help but...“, it's referring to someone's feeling or compulsion, therefore the subject is usually a person. 不得不, on the other hand, is a cognitive decision made based on objective conditions, and circumstances: Compare these two examples: - 不由得 here refers to the compulsion to laugh: E.g. 看着他的滑稽模样，我不由得大笑起来。Seeing his funny appearance, I couldn't help laughing. - 不得不 is followed by a decision that is made based on the situation that the task has to be completed but is yet to be: E.g. 任务还没完成，所以周末我们不得不加班。 The task is not completed, so on the weekend we will have to work extra hours.

1 - '由得'与'不由得'（或曰'由不得'）为语义相对之词。'由得'意指'可由（某人）决断，可由（某人）之言而定'。'不由得'或'由不得'之对立面，即非由某人决定。值得注意的是，'不由得'与'由不得'另有一层含义，即'不禁……'。'不得不'则表示'必须，别无选择或余地'。二者之别在于，当'不由得'与'由不得'表示'不禁……'时，所指涉者通常为个人之情或强制，故主语通常为人。而'不得不'则是一种基于客观条件与环境的认知决策：对比以下两例：- '不由得'在此指笑之强制：例如，看着他滑稽的模样，我不禁大笑起来。- '不得不'之后随决策，此决策基于任务尚未完成但必须完成的情境：例如，任务尚未完成，因此我们周末不得不加班。