1. ～てしかたがない / ～てたまらない (So... / Unbearably...)
I-adjective い -> くて + しかたがない / しょうがない / たまらない
Na-adjective だ -> で + しかたがない / しょうがない / たまらない
Meaning: Expresses an emotion, desire, or sensation so strong that it feels uncontrollable: “so... / unbearably...”.
✓ ～てしかたがない / ～てしょうがない describe a strong state the speaker cannot easily control; ～てしょうがない is more conversational.
✓ ～てたまらない strongly means “unbearably” and is common with physical sensations, though it can also describe emotions.
✓ For a third person’s inner state, Japanese normally uses observable/inferential marking such as らしい, ようだ, そうだ, or another contextually appropriate construction.
2. ～てならない (Cannot help feeling... / Extremely...)
I-adjective い -> くて + ならない
Na-adjective だ -> で + ならない
Meaning: ～てならない describes a feeling, thought, or impression that arises spontaneously and cannot be dismissed: “cannot help feeling / extremely...”.
✓ Common with expressions such as 気がする, 思える, 思い出される, 心配だ, 残念だ.
✓ It is not limited to negative emotions, although worry and regret are common.
✓ When describing a third person’s inner state, an appropriate inferential/observational expression is normally required.
3. ～ないではいられない / ～ずにはいられない (Cannot help but... / Cannot resist...)
* Ngoại lệ: Động từ する -> せずに
Meaning: ～ないではいられない / ～ずにはいられない means “cannot help doing / cannot refrain from doing”. An emotion, urge, or spontaneous reaction leads to the action.
✓ ～ずにはいられない is somewhat more formal/written. With する: せずにはいられない.
✓ With a third-person subject, evidence or information-source marking such as そうだ, ようだ, or らしい is often needed depending on context.
4. ～ないわけにはいかない (Cannot avoid doing / Must...)
Meaning: ～ないわけにはいかない means “cannot avoid doing / have no choice but to do”. Responsibility, circumstances, social expectations, or practical necessity make “not doing it” unacceptable.
✓ It commonly occurs with intentional actions.
✓ There is no absolute rule that a third-person subject is impossible; however, another person’s internal obligation normally requires suitable context or marking.
✓ Contrast ～わけにはいかない: “cannot do...” because of social, moral, or situational constraints.
5. ～ざるを得ない (Have no choice but to... / Be forced to...)
* Ngoại lệ: Động từ する -> せざるを得ない
Meaning: ～ざるを得ない means “be compelled to / have no choice but to...”. Circumstances or objective grounds force the subject to take an action even if it is undesirable.
✓ It is stiffer and more formal than ～ないわけにはいかない and is common in writing, news, and formal explanation.
✓ The subject does not have to be first person. With する: せざるを得ない.
