At a glance
必ずしも～とは限らない means "not necessarily" or "not always". Use it to say that something people usually expect is not true in every case.
必ずしも + [plain form] + とは限らない
必ずしも高いものが良いとは限らない。 Expensive things are not necessarily good.
How to form it
とは限らない attaches to the plain form:
| Attaches to | Example | Meaning |
|---|---|---|
| Verb | 行くとは限らない | (someone) won't necessarily go |
| Verb (negative) | 行かないとは限らない | it's not certain (someone) won't go |
| Verb (past) | 行ったとは限らない | (someone) didn't necessarily go |
| い-adjective | 高いとは限らない | not necessarily expensive |
| な-adjective | 便利だとは限らない / 便利とは限らない | not necessarily convenient |
| Noun | 学生だとは限らない / 学生とは限らない | not necessarily a student |
With nouns and な-adjectives, だ can be dropped. For polite speech, change the ending to とは限りません.