とは限らない
Not necessarily so, Is not always true, There is no guarantee that
Structure
［い］Adjective + とは限らない
［な］Adjective + だ + とは限らない
Noun + だ + とは限らない
Explanation
とは限らない is a phrase that expresses that something 'is not always the case', or 'is not necessarily true'. This structure is formed using the case marking particle と to indicate a conclusion, the adverbial particle は for emphasis, and the negative conjugation of the う - Verb 限る, meaning 'to limit'.
This grammar point can follow verbs, い-Adjectives, な-Adjectives, and nouns. However, だ is required when this structure follows な-Adjectives and nouns.
- 毎日運動しているからといって、痩せるとは限らない。Just because you exercise every day doesn't guarantee that you will lose weight.
- 高いものがいつでも良いとは限らない。Expensive things are not necessarily always good.
- 大きな町がいつも便利だとは限らない。A big city is not necessarily always convenient.
- 有名なブランドだからといって、必ずしも高品質だとは限らない。Just because it's a famous brand doesn't necessarily mean it's high quality.
限らない literally means 'not restricted to' or 'not limited to'. As such, while と points to a specific outcome, that outcome is then clarified as being 'not the only possibility'.
Examples
高い物がいつも良い物だとは限らない。
Just because something is expensive doesn't necessarily mean it's good quality.
天気予報が晴れでも、雨が降らないとは限りません。
Even if the weather forecast says it will be sunny, there is no guarantee it won't rain.
努力すれば必ず成功するとは限らない。
Just because you work hard, there is no guarantee that you will succeed.
新聞に書いてあることが、いつも真実だとは限りません。
What is written in the newspaper is not necessarily always the truth.
強いチームがいつも勝つとは限らない。
The strongest team does not necessarily win every time.
新しいものが常に良いとは限りません。
Something new is not necessarily better.
日本に住んでいれば日本語が上手に話せるとは限らない。
Just because you live in Japan, it doesn't necessarily mean you can speak Japanese well.
便利なものがいつも必要だとは限らない。
Just because something is convenient doesn't necessarily mean it's necessary.
笑っている人が、いつも楽しいとは限らない。
It is not always true that people who are smiling are happy.
有名なレストランの料理がいつでもおいしいとは限らない。
Food from a famous restaurant isn't always delicious.
体に良いものでも、食べすぎれば安全だとは限らない。
Even if something is good for your body, it's not necessarily safe to eat too much of it.
人気がある商品が自分に合うとは限らない。
A popular product won't necessarily suit you.