Recently I came across the question of translating the word “unlock” into another language.  In Vietnamese the word would be translated “mo khoa” or “open lock”.  This got me thinking why they didn’t just use the word “lock” with another word that means to undo, the same function as “un-” in English.

When I thought about it further I realized that, although “un-” can be used for adjectives and verbs, it can be used for most adjectives but only a handful of verbs.  For example, we can unlock, undo (at least in the computer age), unfasten, unbutton, unzip, undress, or unleash but we cannot undrive, unhit, unpay, unclose, or uneat.  And we can only un-break my heart in certain songs.

So what’s the difference between verbs that can take un- and the verbs that cannot?  Well, all the verbs in the first list represent actions that change the state of something that can only be in two states.  For example, a lock can be locked or unlocked, a seatbelt can be fastened or unfastened, and I can be dressed or undressed but I can dress and undress and then dress and undress ad infinitum.  In fact, all those verbs can also take the prefix re-, for example, re-lock, re-fasten.

For adjectives, the prefix un- basically means “not”.  So unpopular means not popular, unintelligent means not intelligent, unusual means not usual, undressed means not dressed, and unlocked means not locked.  But why don’t we say unpossible, unbalanced, unregular, unaccurate, or unnumerable?  Instead we say impossible, imbalanced, irregular, inaccurate, and innumerable because Latin used im-, in-, and ir-instead of un- depending on the first letter of the word.

And we have some other prefixes that have the same meaning of “not”: a-, de-, and dis- (which comes from a Latin word similar to “dual”).  Sometimes dis- is used used for verbs where otherwise un- may have worked.  For example, disconnect and disappear.

But I still have another question.  Just as the Vietnamese open locks instead of unlocking them, why do we open doors but don’t un-open them?  Or why do we open windows instead of un-closing them?