Phrase
if not
甚至可能；或许甚至
perhaps, suggesting that something is possibly even more so than stated
- 1.
perhaps; indicating possibility of being more remarkable (greater or better or sooner) than
也许；表示可能比...更突出(更大、更好或更早)
也许；表示可能比...更突出(更大、更好或更早)
In use
You should apologize to her; if not, she will never forgive you.
We must leave now, if not we'll miss the last train.
He needs to study harder; if not, he will fail the exam.
If not, [result clause]
此处'if not'意为'否则'，通常用于句首或分句首。
You should study harder; if not, you might fail the exam.
你应该更努力地学习；如果不的话，你可能会考试不及格。
If not for [noun phrase], [result clause]
此处'if not for'引导一个虚拟条件，意思为'如果不是因为'。
If not for the rain, we would have had a picnic.
若非下雨，我们本可以野餐。
Common mistakes
If not work hard, you will not succeed.If you do not work hard, you will not succeed.
中文习惯用“如果不”直接加动词，但英语中if not不能直接引导无主语的从句，需补全完整if从句结构。
Hurry up, if not you'll be late.Hurry up, or you'll be late.
if not不可用作连词表示“否则”，此义应用or或otherwise，if not常用于省略结构如“if not already”而非引导后果句。
Connections
Learner notes
Grammar Note
常用于条件句或建议句中，表示否则或如果不。
Dictionary facts from ECDICT, WIKTIONARY.