nuances - what is the difference in the usage of [成]{な}るべく and でき るだけ?

Hi guys what is the difference in the usage of 成るべく and できるだけ?

Don't they both mean as [x] as possible?

E.g.:

1) できるだけ多くの本を読みなさい vs なるべく多くの本を読みなさい

2) できるだけ早くお願いします vs なるべく早くお願いします

Answer

I think スコット's answer isn't that off the mark.

If you take なるべく and できるだけ word for word, they become:

成る《なる》 become + 可し 《べし》 must: something must become so-and-so

できる is capable + だけ amount: you do so-and-so as best as you can

See how the subjects are different. なるべく just says that some state should be reached, while できるだけ demands you to make maximum effort in achieving the goal.

This difference isn't much noticeable when used in first person, because the speaker is the one who needs to take action.

However, under an imperative context, できるだけ gets all the more demanding for requiring the other person's effort. So なるべく sounds softer and more appropriate when you're not in a position to demand effort from the listener.

This is how I visualize these two adverbs.

Again, the difference in nuance between the two is very subtle, and they're interchangeable most of the time, if not always.