Hi everybody,
Tell me how you learn prefixes in- and un-? Is there a hint, a rule, helping to learn words with these two prefixes, to divide them into to columns? I need to feel a rule while learning, I need understanding. But here i don’t know what to do…

I found at this link that “in” is the Latin prefix, while “un” is the English prefix. … legal.aspx

Now you just have to memorize which English words come from Latin! :wink:

***** NOT A TEACHER *****

Hello, Akeli:

I believe that many people give this advice: If you try to memorize rules about these prefixes, you will go crazy. The best (and only?) thing to do is to read

widely and notice what words are used by good writers, and to use a good dictionary.

I did find, however, some information that may help you (it certainly helped me!!!).

One expert gives these hints (ideas that may give some help):

  1. Some words are interchangeable: inalterable / unalterable, inconsolable / unconsolable.

  2. Some words must take in - or un- : inescapable, intolerant; unusual, unacceptable.

  3. Some words take un- with a verb but take in- with an adjective: undecided vs. indecisive, undivided vs. indivisible.

  4. Un- is often used for words “that are not likely to be of frequent” use: They left the equipment unrepaired; At that point the stream became unnavigable.

  5. Finally, some words have a slight difference in meaning: A course of action was inadvisable but a man in anger is unadvisable. (Un- is often literal; in- is often figurative.)

Thanks for your question. I learned something new today.


  • Credit for this information goes to Wilson Follett in the 1980 edition of his Modern American Usage (pages 335 -336). Published by Avenal Books in New York City.

Thanks, Luschen :slight_smile:
I knew about Latin and English words, but i don’t remember Latin ))))

Thanks, James
your info was so detailed! But it really makes me crazy. I prefer to read more :wink:

And another question-if i say a word with the prefix in-, but it should be un- would it be a very rude mistake? I don’t say about another prefixes but these two seem to be almost similar for me.So then?

***** NOT A TEACHER *****

You are very welcome, Akeli.

Tom: I hate James.

Mona: Why?

Tom: Because he is so old.

Mona: Does his being old affect your life?

Tom: I guess not.

Mona: Well. then, don’t be so intolerant of old people.

If Mona had said “untolerant,” I do not think that she would have

been “rude,” but she would have used incorrect English.

Good luck on your mission to further understand the difference between

“in” and “un.” Please share your findings with us.


Using “un” instead of in would not be “unconspicuous”, but it is not really “unconsiderate” and you would not be considered “unsane”.

Hello, Akeli:

***** NOT A TEACHER *****

It’s I again! (Regular English: It’s me again.)

I found somethng in a huge grammar book used by many teachers throughout the world. I have the 1985 edition. It was written by four experts: Randolph Quirk, Sidney Greenbaum, Geoffrey Leech, and Jan Svartvik. It was published by Longman (with offices in London and New York). The information I found is on pages 1,540 - 1,541. (I told you it was huge!)

Why have I given so many boring details about the book? Well, here in the United States, the copyright laws are VERY strict. Since I have given 100% credit to the book, I THINK that I may BRIEFLY report some of its findings.


a) sometimes it is spelled il-, im-, ir- in some words.
b) it combines with adjectives of French and Latin origin.
c) it is “less common” than un-.


a) “combines fairly freely with adjectives and participles”:

unfair, unwise, unforgettable, unassuming, unexpected.

Those scholars reminded us, too, that sometimes “un-” does NOT mean “not.” It means “reversing the action”: undo, untie, unpack.


Hello James,
I appreciate your such a strict and brief description and your titanic work :wink:
Now I’m working on my own theory and I’m going to share it with you when I find it :slight_smile:
I suppose it’s like a riddle of Einstein :wink:

We all look forward to reading your theory!