Understanding あながち for "not necessarily"

Question

I understand that this phrase is used with a negative to create a "not entirely" or "not necessarily" sentence. But I am having trouble distinguishing it from 必ずしも.

Online dictionaries do distinguish them, but I find trouble understanding how they differ still:

「必ずしも」は、「絶対…というわけではない」「Aならば必ずBというわけではない」など、単なる強調、例外の存在、条件に対する結果、評価などが決まっているわけではないこと、などを表わす。
「あながち」は、そうとばかりは言えないという意で、強く判定することに反対するという意味合いを持つ語。

I feel as if these definitions come out practically to mean the same thing,
but they list how this sentence works for 必ずしも but not あながち:

金持ちだからといって…えらくはない

In short, how do they differ in usage/how does one typically use あながち? Register? Are the familiar phrases used with 必ずしも like わけではない, とは限らない, and からといって also used with あながち? Lastly, might this bit a bit more casual way to say "not necessarily"? I ask because I sometimes feel 必ずしも comes off a bit strong.

Answer 1

必ずしも is an objective or matter-of-fact expression. In academic or technical articles, you should be using this in nearly all cases. Especially in situations where there are objective exceptions, such as "a knife is not necessarily made of metal", you always need to use "必ずしも～ない" (or "～とは限らない").

あながち is much more subjective, and it's very commonly used in combination with ～とは言えない, ～とは思わない, etc. It expresses the speaker's hesitation or reserved attitude, like "It's hard (for me) to definitively say ～". It's typically used with some subjective judgment, like 彼女があながち悪いとはいえないと思う or あながち下手だと否定はできない.

In your example:

• 金持ちだからといって必ずしも偉くはない is an objective statement, "Just because someone is rich doesn't necessarily mean they're great". You're explaining this as a fact.
• 金持ちだからといってあながち偉くはない sounds awkward to me, I expect something like 言う/思う.
• 金持ちだからといってあながち偉いとは言えない is subjective, something like "I don't say I agree with the idea that a rich person is always a great person".

あながち is not casual at all. It's typically used in serious written essays. But あながち can sound more reserved or mild if used appropriately.