わけではない

1. 1It's not that… / It doesn't mean that…: rejects an inference that might be drawn from the situation, often before stating the real reason.Ex. 1
2. 2Softly denies a feeling or state others might assume, then clarifies what the speaker actually means.Ex. 2

Neutral in register and common in both conversation and writing, with わけじゃない preferred in casual speech. It often appears as 〜わけではないが, or is followed by ただ〜だけだ, to correct a misunderstanding and give the real reason. With words like 全部 or いつも it expresses partial negation. Unlike わけがない, which flatly rejects a possibility, it only denies an assumed inference.

• というものでもないN2「というものでもない」 is mainly used to point out that common-sense claims like "the more... the better" or "as long as..., it's fine" don't always hold true, often paired with patterns such as 「〜ばいい」; it is rarely used for making excuses. Its meaning of partial negation is close to 「わけではない」.
• とは限らないN3「とは限らない」 simply means "not necessarily; there are exceptions," focusing on the fact that something cannot be asserted to always be the case; it is generally not used for excuses or introducing a real reason. It is close to sense 2 of 「わけではない」 (partial negation) and the two are often interchangeable. Nouns and な-adjectives take 「（だ）」, not 「な」.
• というものではないN2「というものではない」 specifically negates social common sense or general claims, with a reasoned, argumentative tone, and cannot negate individual concrete facts. It is often used as 「〜ばいいというものではない」 to mean "it's not that things are fine just because...". Nouns and な-adjectives take 「（だ）」.
• ないことはないN3「ないことはない」 is a double negative that gives a reluctant, qualified affirmation of a possibility or state ("it's not that one can't..."). It must be preceded by a negative form, and verbs usually appear in the potential form. 「わけではない」 negates an inference and can also express partial negation, so the two are generally not interchangeable.
• 〜なくもないN2「なくもない」 is a reluctant affirmation ("it's not that there isn't..."), formed by changing 「ない」 to 「なく」 and adding 「もない」; it does not express partial negation. It cannot directly replace 「わけではない」 and is only close in meaning to 「〜ないわけではない」.
• わけがないN3「わけがない」 means "there's no way that...; it's impossible," flatly denying, on the grounds of reason or common sense, that something could hold true, with a much stronger tone; the two cannot be interchanged. With nouns it takes 「の／である」, whereas 「わけではない」 takes 「な／である」.

わけではない rejects an inference, whereas とは限らない stresses that a generalization has exceptions ("not necessarily"), わけがない flatly rules out a possibility, and ないことはない / 〜なくもない are double negatives that give a hesitant, partial affirmation. というものではない / というものでもない reject a general notion or assumption, often critically ("it's not the case that just X is enough"), rather than correcting a specific inference about the speaker.