hadn't
v.v. the short way to say 'had not'. You use it to talk about something that did not happen before a specific time in the past.
v. The contracted form of 'had not'. Used as an auxiliary verb to form the negative past perfect tense.
I hadn't seen that movie before last night.
She realized she hadn't locked the front door only after she arrived at the train station.
The researchers discovered that the participants hadn't been informed of the potential side effects before the clinical trial commenced, leading to a significant ethical review of the study's protocols.
had + -n't
Functions as an auxiliary verb; typically followed by a past participle to form the past perfect negative.
I hadn't went thereI hadn't gone thereAfter 'hadn't', you must use the past participle (gone) rather than the simple past (went).