并不 / 并没有【bìng bù / bìng méiyǒu】

并 before 不 or 没有 makes the negative push back against an assumption: "actually not", "not at all, whatever you think". The assumption may be the listener's, or just what anyone would expect.

With no expectation to contradict, 并 sounds odd: 并不难 answers someone who thinks it's hard. It often comes with 其实, 但是 or 可是.

并不 or 并没有

The choice follows the usual split. 并不 negates a state, a habit or a view. 并没有 (or 并没) says an event didn't happen.

• × 我并不有时间 → 我并没有时间
• × 他昨天并不去 → 他昨天并没有去

Where 并 goes

并 sits right before 不 or 没, after the subject and any time word.

• × 并他不知道 → 他并不知道
• × 他不并知道 → 他并不知道

并不是…而是

With 是, the frame corrects one explanation and supplies another. The formal written form is 并非.