Given the different questions we have seen about the prefixes "de-" and "un-", I have grown curious if there is a overarching rule for terms that need undoing.

For actions taken that need to be revoked or reversed, which prefix is preferred? Is there a distinction created by the underlying terms? Is it purely a usage issue where the one most used is the one to use? Do "un-" and "de-" actually have different meanings such that both could help determine which is most appropriate?

  • Lady MacB: "desex me here?" Hmmm. May 18, 2011 at 18:37

3 Answers 3


Some prescriptive grammarians would argue that the de- prefix should be used on verbs and un- should be used on adjectives.

So, you deregister something and it becomes unregistered, or you deselect something and it is now unselected.

The logic behind this is probably because de- only attaches to verbs to give the notion of reversal, so for the sake of order/non-redundancy/etc. you'd want un- to occupy the other domain: yielding the opposite meaning of an adjective it attaches to, and nothing else.

However, it has never really worked this way; the prefix redundancy among verbs is there, and it is very unlikely to disappear. Note that, most of the time, you can't just use whichever one you want — usually there is one preferred form. But whether it is un- or de- is something that varies on a word-by-word basis.

FumbleFingers mentioned something else in comments that is worth mentioning: un- seems to be much more widespread, even in the verbal realm, in the production of new words in the past few decades.

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    Until recently "un-" as a verbal prefix was quite limited in the class of verbs it would attach to: those of closing, fastening, wrapping only (with rare exceptions like "unsay"). It was still productive, but only within that semantic field. Recently, particularly in the computer world, it has become more productive, probably as backformations from participles with "un-".
    – Colin Fine
    May 18, 2011 at 17:05
  • @Kosmonaut: Excellent summary of both the position and the rationale. But I suspect the deselect/unselected pairing may actually become significantly less 'preferred' over time, simply because modern computer screens force us to juxtapose the two words far more often than we used to. People will opt for one prefix over the other in both forms. Whatever - I doubt we'll see much of a rise in the use of decheck paired with unchecked in the coming years. May 18, 2011 at 17:15
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    @Colin Fine: I've heard this said, but I wonder how true this actually is — I think this is another prescriptive attempt to retain neat categories for these prefixes in spite of contrary evidence. Just looking through the OED for verbs occurring pre-20th century that begin with un-, I see lots of words: unalchemy (1661), unanchor (1648), unappoint (1682), unarm (1470), unassure (1643), unavail (1866), unbalast (1769), unbaptize (1611), unbeautify (1570), unbed (1611). This is just a selection from among the first few pages of the 1300 results.
    – Kosmonaut
    May 18, 2011 at 17:44
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    @Kosmonaut: Productive? It's positively fecund! Actually, I quite like the way we all routinely talk about the undo function nowadays. May 18, 2011 at 17:55
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    @Kosmonaut: maybe you're right about the productiveness of "un-" with verbs, but I'm dubious. I'm aware of the semantic restriction because I read about it in Whorf (one of his examples of "cryptotypes") not because I have ever been taught it. "Unsay" sounds distinctly odd to me. I agree that it has become much more productive recently.
    – Colin Fine
    May 19, 2011 at 16:22

Very broadly, de- is more likely to indicate action, whereas un- is more likely to connote a passive status: After you detune your guitar, it is an untuned guitar.

In practice, of course, there are so many exceptions and counterexamples as to render this "rule" largely meaningless. I would guess, though, that people are somewhat more likely to follow this convention than the opposite when coining ad-hoc new words from existing roots (example: to deselect a check box in a computer GUI is an action, whereas unselected is a status that the box can have).


Among verbs, I believe that un- is used to intrinsically undo something (eg, uncreating an object) whereas de- means to reverse its effects (eg, decompiling a program), without modifying the original item.


  • One might want to unsay something—to take back the fact that it was said in the first place.

  • People become desensitized to things—their sensitivity is nullified.

  • People become demotivated—their motivation is reversed.

  • People unsubscribe from email lists—they get rid of their subscription

  • People unwrap things—they get rid of the original wrapping

  • Arguments are deconstructed—they are broken down and attacked; the argument itself is not destroyed.

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    Nice job at trying to fill in a gap in the other answers! This is especially noteworthy because those other answers are good and accurate responses to the question, so much so that I didn't even realize there was more to say until you offered this! I can't verify that your hypothesis is correct, but it was still worth mentioning.
    – John Y
    May 18, 2011 at 22:37

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