Is there any difference between 相濡以沫 and 以沫相濡?

Question

I encountered the following sentence:

他们都一直相濡以沫，患难与共。

I looked up the entry on Pleco, and although it shows the meaning, it also redirects toward 以沫相濡, which seems to have the same meaning (as well as 濡沫).

So I wonder whether it is OK to assume that these are just synonyms and have no difference, or have any meaningful (even if tiny) difference.

Also, is this kind of Chengyu (the first and last two characters are flipped) common? And if it is practically same, why do these different forms exist in the first place?

Answer 1

1. They have the same meaning, even the point of emphasis might be subtle different. For "以沫相濡", the emphasis is placed more on "以沫";

2. Chinese often change the order of characters or use abbreviation for matching words in same sound, sense or number of characters, especially in poem or libretto; e.g.

   宋．范成大．次韻龔養正病中見寄詩：「激水要令風在下，涸泉翻以沫相濡。」
   鲁迅 《题〈芥子园画谱〉三集赠许广平》诗：“十年携手共艰危，以沫相濡亦可哀。”
   韩愈 叉鱼招张功曹：濡沫情虽密，登门事已辽。
   柳宗元 酬娄秀才将之淮南见赠之什：好音怜铩羽，濡沫慰穷鳞。

3. The original words from 《庄子》 is 相濡以沫, which is used generally; 以沫相濡 is seldom used.

Answer 2

Also, is this kind of Chengyu (the first and last two characters are flipped) common? 

No, it's not common.

相濡以沫 is the most people would use. 以沫相濡 is not that common, though we can understand it.

We don't usually flip the character order in idioms.

Answer 3

They are just variants of one another - with no real differences in meaning.

Although 相濡 and 以沫 technically aren't real words, you can split them up into two different phrases. Often these kind of phrase types are easily moved around or changed in phrases, expressions and the type.