Put in- in front of a word and you often get its opposite: correct and incorrect, visible and invisible. All ten words in this topic are built that way. Each one is a no: impeccable is not able to go wrong, insatiable is not able to be filled up, irrevocable is not able to be called back.
Key idea
in- = not. To be easier to say, it changes its last letter to match the sound after it: im- before b, m and p (impeccable), il- before l (illegal) and ir- before r (irrevocable). Many of these words end in -able or -ible, so they mean not able to be…
Peel off the in- and look at what is left. Sometimes it is a word you know (correct, apt); sometimes it is a Latin word worth learning (satis, enough; nocere, to harm). The memory hooks below lean on those parts.
The ten words
The roots at work
Common mistake
Not every in- means not: inflammable means easily set on fire, and invaluable means priceless. The in- that means not becomes im- before b, m and p, il- before l and ir- before r.
| word | built from | so it means |
|---|---|---|
| impeccable | im- + peccare, to sin | not able to go wrong: flawless |
| inept | in- + aptus, fit | not fit for the job: clumsy |
| inert | in- + ars, skill | idle: not moving |
| indomitable | in- + domitare, to tame | not able to be tamed or beaten |
| inexorable | in- + exorare, to win over by pleading | not moved by pleading: unstoppable |
| insatiable | in- + satis, enough | never full |
| innocuous | in- + nocere, to harm | harmless |
| incorrigible | in- + corrigere, to correct | not able to be corrected |
| inscrutable | in- + scrutari, to search | not able to be searched out: mysterious |
| irrevocable | ir- + revocare, to call back | not able to be taken back |
Watch the spelling change. Before p, in- becomes im- (impeccable, impossible); before r, it becomes ir- (irrevocable, irregular), which is why those words have a double r. Before l it becomes il- (illegal, illogical).