とは限らないNot necessarily; not always
とは限らない says that a general rule, expectation, or prediction is not guaranteed to be true in every case. It leaves room for exceptions rather than directly asserting the opposite.
What the construction corrects
Use this construction when someone might treat a claim as applying to every case. Words such as 必ず, いつも, 全部, すべて, and 誰でも often make that broad expectation explicit. The point is not that the claim is false; it is that exceptions may exist.
Across different sentence types
The complete statement comes before the construction. Notice especially the retained だ with nouns and na-adjectives.
努力すれば必ず報われるとは限らない。
Hard work does not necessarily always pay off.
Analyze値段が高い商品が、いつも長持ちするとは限らない。
Expensive products do not always last a long time.
Analyze便利な方法が誰にとっても安全だとは限らない。
A convenient method is not necessarily safe for everyone.
Analyze有名な人がその分野の専門家だとは限らない。
A famous person is not necessarily an expert in that field.
AnalyzeChoosing among nearby forms
とは限らない focuses on exceptions or lack of guarantee. わけではない more broadly corrects an interpretation and does not require an all-cases claim. というものではない evaluates a proposed rule or criterion as too simplistic. かもしれない simply presents an individual possibility, while the target construction starts from a claim that might otherwise be treated as certain or universal.
More examples
若い人がみんな新しい技術に詳しいとは限らない。
Not all young people are knowledgeable about new technology.
Analyze経験が多ければ、判断が正しいとは限らない。
Having a lot of experience does not necessarily mean that one's judgment is correct.
Analyze無料のサービスが本当に得だとは限らない。
A free service is not necessarily a good deal.
Analyze説明書を読めば、誰でもすぐ使えるとは限らない。
Reading the instructions does not guarantee that everyone will be able to use it right away.
Analyze精度が高くても、天気予報が外れないとは限らない。
Even highly accurate weather forecasts are not guaranteed to be right.
Analyze静かな場所が必ずしも集中しやすいとは限らない。
A quiet place is not necessarily one where it is easy to concentrate.
Analyze