What is 匪 in 受益匪浅?

Question

In 受益匪浅 does 匪 just mean 非?

If I look up 匪 I get: bandits, robbers, gangsters.

受益匪浅: gain 受益 not 匪 little 浅: an ideological gain?

Answer 1

Here, modern researchers consider 匪 in 受益匪浅 as an interchangeable character of 非, which means apparently 不(no, not).

To point out, the English term "interchangeable character" does NOT mean that we can really change them, like replacing 匪 in 受益匪浅 with 非. "Interchangeable character" here is a translation of a proper noun of a concept in Chinese linguistics, which is called "通假字" in Chinese.

This concept suggests that in the past, some "wrong" characters were used for like, whatever reason. Usually, it's just a mistake made by the ancient writer. But the second possible reason, which is also a common case, is due to an ancient Chinese custom called "避讳", which no longer exists since 1912. This custom forbids strictly the use of any characters presented in the names of the current dynasty's emperors, just like taboos. No matter what exactly the reason of the misuse was, we, the modern Chinese users, just keep them in its "wrong" way.

Thus, since lots of chengyus in modern Mandarin are in fact inherited from the old Chinese, surely there are a lot of 通假字(interchangeable characters). As a matter of fact, even native Chinese speakers can have difficulty distinguishing between interchangeable characters in certain chengyus, since in a sense, they're indeed wrong characters.

All I can tell you is that in particular, 匪 here is an interchangeable character of 非. But in general, it could be really hard to determine whether a character is an interchangeable character or not. Judging this is a professional work field of textual criticism in Chinese linguistics, where I'm not an expert at all.

For those who don't learn Chinese for a linguistic research, to check if a character is an interchangeable character in a particular chengyu can simply be done by using Google or Baidu("the Chinese Google"). This works in most of the time. Without relying on the internet, determining this can also be done by testing characters that look similar to the one that you suspect. The reason for this is that most interchangeable characters tend to look similar, with another small part also sound similar. Cases where neither of these 2 aforementioned cases are applicable are extremely rare.

Hope that I've helped you, nice day~

Answer 2

匪 means 不 (not, no) here

受益匪浅 learned a lot, gained a lot of knowledge