とは限(かぎ)らないNot necessarily so, Is not always true, There is no guarantee that

Both とは限らない and わけではない challenge assumptions, but in different ways. わけではない denies a specific inference or interpretation, e.g. 'it's not the case that (A)', while とは限らない emphasizes exceptions, e.g. 'just because (A), it's not always (B)'.

These two expressions are similar in meaning, but with a slightly different nuance. とは限らない says that something isn't necessarily the case, e.g. '高いものが必ずしも良いとは限らない' ('Expensive things aren't always good'). というものでもない says that something cannot be stated as a general truth, e.g. '努力すれば必ず成功するというものでもない' ('It's not necessarily true that effort always leads to success').

Both introduce nuance and uncertainty, but with opposite slants. とは限らない expresses that something isn't necessarily the case, e.g. '有名だからといって面白いとは限らない' ('Just because it's famous doesn't mean it's interesting'). ないことはない uses a double negative to express a less confident positive statement, e.g. '行けないことはない' ('It's not that I can't go').

Both expressions deny absolutes, but differ in usage. とは限らない expresses that something isn't necessarily the case, e.g. '留学すれば英語が上手になるとは限らない' ('Studying abroad doesn't always mean your English improves'). というわけではない clarifies previous statements or assumptions, e.g. '嫌いというわけではない' ('It's not the case I dislike it').

必ずしも and とは限らない often appear together as a pair in statements expressing that something isn't necessarily always the case, e.g. 必ずしも努力が報われるとは限らない ('Effort doesn't always pay off.'). とは限らない alone can express the same meaning without 必ずしも, but the pairing goes together naturally.

While both deny expected conclusions, ことにはならない expresses that one thing doesn't necessarily lead to another, e.g. '話し合ったからといって解決したことにはならない' ('Just talking about it doesn't mean it's resolved'). とは限らない expresses that something isn't necessarily the case, e.g. '高いものが必ずしも良いとは限らない' ('Expensive things aren't always good').

These two expressions derived from 限る contrast in meaning. とは限らない expresses that something is not necessarily the case, e.g. '雨だからといって中止とは限らない' ('Just because it's raining doesn't mean it will be canceled'). 限り indicates a bounded condition or extent, e.g. '知っている限り' ('as far as I know').