What is the difference between 〜となる and 〜になる?


Is it a nuance difference? Is it formality?

**EDIT**

For example:

> 請求書のお支払いは現金のみとなりますので、ご了承くださいませ。
>
> 請求書のお支払いは現金のみになりますので、ご了承くださいませ。

I just made that example up, but for some reason, my gut tells me it's the
first one, even though I don't see anything grammatically wrong with the
second, either. Is it formality level only?




Pretty finely nuanced, I'd say. と is a quotative particle, but is also used to
described the manner in which something is done, often figurative. ～となる can be
used to mean "become like a ~" while ～になる is literally "become a ~".




I've asked this very question in the past and my research led me to the
following definition which (surprisingly) differs from every other answer here
so far:

**～となる expresses a discrete change, while ～になる can express either a discrete
or a continuous change.**

You can feasibly use ～になる for everything, since it covers all cases, but in
cases where you want to use the most suitable grammatical phrasing (such as in
formal situations), you often see this distinction made.

Examples:

> その島は去年、無人島 **となった** 。 (～となる because the change from "inhabited" to
> "uninhabited" is discrete and happens the instant the last person leaves.)
>
> デビューした後、彼はだんだん人気者 **になっていった** 。 (～になる because popularity changes
> continuously in unmeasurable steps.)
>
> スカイツリーは現在、日本一高い建造物 **となっている** 。 (～となる because the title of "tallest building
> in Japan" applies to exactly one building, and a building cannot gradually
> become the tallest. It either is or it isn't.)
>
> 季節はこれから夏 **になっていく** 。 (～になる because the change in seasons is a gradual,
> progressive one.)
>
> 電線事故のため、新山口駅は終点 **となります** 。 (～となる because the title of "terminal station"
> only belongs to one station, and a station can't hold it partially.)

Your example in the question illustrates a discrete change in state (or more
precisely, a discrete difference between 現金 and all other forms of payment),
so both ～となる and ～になる are acceptable. However, since ～となる is "built" for such
situations as these, it sounds more "proper" to use ～となる.

I suspect this rule also applies to the ～とする and ～にする forms, but I would have
to do more research to confirm this.

