Now for some bad news: There is no foolproof (= 100% certain) way to know whether you can make a negative word with –in or –un. Some words take –dis for the negative! For instance, the opposite of honest is dishonest.

However there are two rules that you can use.

Rule 1: Words with –able at the end have –un.

For example:

comfortable – uncomfortable

able – unable

forgettable – unforgettable

countable – uncountable

drinkable – undrinkable

readable – unreadable

recognizable – unrecognizable

forgivable – unforgivable

liveable – unliveable

believable – unbelievable

suitable – unsuitable

Rule 2: When a positive word starts with –in or -en, the negative of that will not be –in.

So there wouldn’t be any words that start with inin- or inen-. You’ll have to admit that would sound really silly, wouldn’t it?

Examples:

intelligent – unintelligent

enlightened – unenlightened

engaged – unengaged

install – uninstall

What’s the Best Way to Learn these Negative Words?

I advise that you first look at a number of un- and –in words, just to make you aware that they exist. If you can remember them all in one go, that’s great. You have a photographic memory! If you don’t, that’s perfectly normal.

Then the second thing you can do is use Word Spellchecker. Let’s look again at the two words from the title. Should it be unforgettable or inforgettable?
Suppose I’ve forgotten my –able rule. So I try typing inforgettable in Microsoft Word. It gets a red squiggly line under it. So that’s the incorrect word. It should be unforgettable.

Yes, but you will say that Spellchecker makes mistakes sometimes or chooses the wrong word for you. That’s true, but trust me, about –in or –un it’s never wrong, as far as I’ve been able to verify (= check).

Here is a small word list that I’d like you to go over, and perhaps remember them — if you can. These words are really common:

Hint: if the word is simple and common, it will take –un for the negative.

Common – uncommon

Do – undo

Dress – undress

Clean – unclean

Happy – unhappy

Able – unable (and all the words with –able are like this, as we learned in Rule 1)

Real – unreal

Equal – unequal (but inequality)

Discreet – indiscreet

Appropriate – inappropriate

Active – inactive

Edible – inedible

Convenient – inconvenient

Decisive – indecisive

Conclusive – inconclusive

Effective – ineffective

Correct – incorrect

Efficient – inefficient

Tolerant – intolerant

Sensitive – insensitive

Have you got those? You’re too good!

So now we can do an exercise.

Exercise

I recommend you do this online, because then you’ll be able to check your answers.

Choose the negative form of one of the following words:

decisive, efficient, correct, able, edible, engaged, suitable, happy, recognizable, comfortable

1 Testing students’ reading ability by giving them a text that is too difficult for them is ____________.

2 Those cucumbers have turned grey. In fact, they look pretty _____________.

3 – Isn’t Patsy married? – No, she’s still ____________.

4 I’m sorry to have made you ___________. I’ll buy you flowers tomorrow.

5 Wearing dark sunglasses and a hat Mr Turner looks ____________.

6 Nashat apologized that he was ___________ to make it to the meeting on time.

7 The airplane seats have been shrunk to the size of a child’s bottom. They’re terribly ___________.

8 What’s it going to be: an orange and mango shake or bananas and strawberries? Don’t be so ____________!

9 If I add up the numbers I get another total. There must be an __________ calculation somewhere.

10 Usually new managers are pretty useless because they want to make clean house. However our new manager set a new record in being totally ___________.