Word building: Prefixes

Prefixes can be quite confusing. Although some languages make use of prefixes like un- or in- to form negative adjectives, mentally translating from one language to another won’t always help you get it right.

The use of unsensitive instead of insensitive is a common mistake – here’s why:


Not only do Swiss or German speakers have to keep false friends in mind – they also have to think about whether the prefix changes or not in English. Adjective prefixes might sometimes correspond in different languages, but you can’t always rely on translation. Using German as an example, here are a few adjectives with the prefix in-.


Only one adjective changes its prefix from in- to un- in English – so far, so good. However, things get a little more complicated when it comes to translating German adjectives prefixed with un-.

unabsichtlichunintentional or involuntarily
unglaublichunbelievable or incredible
unlesbarunreadable or illegible

As you can see, un- is sometimes replaced with in-, ir-, im-, or il- in English. Listeners will still get what you mean if you say un- instead of insensitive, so isn’t such a big deal. However, figuring out which prefixes differ between English and your first language will help you become more accurate when speaking. You might get it wrong again, but don’t worry – being aware you’re making a mistake is the first step towards fixing it.

When to use in-, ir-, im- or il-

Some adjectives in English can be combined with the prefix in-, however, it is sometimes replaced with ir-im-, or il-, depending on the following consonant.

Before r: ir-

irregular, irresponsible, irredeemable, irreparable, irresistible, etc.

Before p: im- 

impossible, impractical, imperfect, impermanent, implausible, etc.

Before l: il-

illegible, illegitimate, illogical, illegal, illiterate, etc.

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