So / Not as Substitutes for a Clause
Level B1 · Conjunctions & Linking Words
After certain reporting and opinion verbs — think, hope, guess, believe, expect, suppose, be afraid, tell — English can avoid repeating a whole clause by replacing it with so (for a positive answer) or not (for a negative one). Will it rain? I think so replaces I think it will rain; will it rain? I hope not replaces I hope it won't rain — so and not each stand in for the entire clause that was just mentioned.
How so and not replace a clause:
- so replaces a positive clause after verbs like think, hope, guess, believe, expect, suppose, imagine: Is she coming? — I believe so (= I believe she is coming).
- not replaces a negative clause after the same verbs, in place of a full negative sentence: Is she coming? — I hope not (= I hope she isn't coming).
- A few verbs (hope, be afraid) only use not for the negative and never add n't to the verb itself: I hope not (never I don't hope so meaning the same); I'm afraid not (a polite way to say no).
- Other verbs (think, believe, guess, suppose) more commonly negate the main verb instead of using not, especially in speech: I don't think so is more natural than I think not, though both exist.
The most common mistake is repeating the full clause after these verbs when so/not would sound far more natural — Will it rain? I think it will rain is grammatically fine but unnaturally repetitive; native speakers say I think so. A second mistake is negating the main verb with hope and be afraid, which only ever take not — I don't hope so and I'm not afraid so are wrong; the negative is I hope not and I'm afraid not. With think, believe, guess and suppose the opposite holds: negating the main verb is the everyday choice, so I don't think so is more natural than I think not.
Look for a yes/no question or a previous statement followed by a short opinion-verb reply (think, hope, guess, believe, expect, suppose, afraid) — if the reply agrees with a positive idea, use so; if it agrees with a negative idea, use not (or don't + think/believe/etc. + so).