東西本身混了別的成分
最字面的一支：杯子裡真的多了東西。
adjective · B2
Not pure or clean, because other things are mixed into it that should not be there, so it is no longer just one substance.
不純的
核心畫面
One way to hold it: a glass that should hold one thing only, and something else has got into it. You do not always see the extra thing, but it is there, and it means what you have is no longer only what it says on the label.
可以想成一只杯子，本來裡面只該有一種東西，結果混進了別的。那個多出來的東西不一定看得見，但它在裡面。所以你手上的東西…更多收起
可以想成一只杯子，本來裡面只該有一種東西，結果混進了別的。那個多出來的東西不一定看得見，但它在裡面。所以你手上的東西，已經不只是標籤上寫的那一樣了。每一種 impure 的用法，都可以看成這個畫面換一個場景。From the word’s history
From Middle French impur, from Latin impūrus. The Latin word is the negative of pūrus (pure), so the word has carried the same shape of meaning — not pure — the whole way into English.
來自中古法文 impur，再往前是拉丁文 impūrus。impūrus 就是 pūrus（純的）加上否定，所以「不純」這個意思一路沒有變過。
Wiktionary entry supplied in this packet (source_ref kaikki:3f6f69a190036ae4:323977588), etymology_text: From Middle French impur, from Latin impūrus.
Three branches
人或行為在規矩上不乾淨
把那只杯子換成一個人：混進來的不是雜質，而是碰到了規矩不許碰的東西，或是心裡的罪。看得見的髒沒有變，但「純」已經破了。
adjective · C1
Unclean in a religious or moral way — made so by touching something forbidden, or by guilt and wrongdoing — rather than dirty in an ordinary way.
不潔的／被玷污的
程式裡會動到外面的東西
程式領域把這個舊字借去，量的還是同一件事：這段程式裡有沒有混進「算答案」以外的動作。
adjective · C1
In programming: describing a function or method that does more than work out an answer — it also changes something outside itself, such as a file, a screen or a stored value.
不純的（函式）