conjunction
Conjunction used to present an alternative or consequence, often with a warning or strong suggestion. Common in both spoken and written Japanese.
急いでください、さもなくば遅れますよ。
Please hurry up, otherwise you'll be late.
もっと勉強しなさい。さもなくば試
Study harder. Or else you'll fail the exam.
More formal and explicit; literally 'if it is not so'. さもなくば is more concise and slightly literary.
Casual spoken alternative; often used in everyday conversation. さもなくば is more emphatic and can sound more serious.
Derived from さも (in that way) + なくば (classical conditional negative of ない). The form なくば is an older equivalent of modern なければ.