Prefix · formal negation
Formal Latin-origin negation with four phonetic forms: invisible, impossible, illegal, irregular.
Written by Bryan López, English teacher · Updated
In- means "not" or "without": it takes away the idea of the word that follows. It has four forms (in-, im-, il- and ir-), which change depending on the letter that comes next to make it easier to say. All four mean exactly the same.
English has two prefixes to say "not": in- and un-. In- is used with words of Latin or French origin, and un- with words of Germanic roots. There is no perfect rule, but it helps to know that words ending in -ible, -able, -ive or -al usually prefer in-. When in doubt, check the dictionary: almost no word accepts both.
The form of the prefix depends on the first letter of the root:
The choice of variant is automatic and phonetic, not grammatical. Forms are never mixed: "inlegal" and "irpossible" do not exist.
in-/im-/il-/ir-/ɪn/, /ɪm/, /ɪl/, /ɪr/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
Before "p" and "b" the prefix is always im-, never in-. The rule is phonetic: "inpossible" is difficult to pronounce fluidly.
"Illegal" is the only standard form. "Unlegal" does not exist. The root "legal" is Latin, so it takes in- (here in its il- variant).
A trick to remember it
The four forms (in-, im-, il-, ir-) all mean "not", and they change only so the word flows smoothly into the next letter. invisible, impossible, illegal, irregular.
Exercise 1 · Form the word
Exercise 2 · Pick the right one
Which is the correct negation of "responsible"?
Exercise 3 · Pick the right one
"She was ___ to wait any longer and left without signing the contract."
The prefix in-/im-/il-/ir- formal Latin-origin negation with four phonetic forms: invisible, impossible, illegal, irregular.
The prefix in-/im-/il-/ir- is pronounced /ɪn/, /ɪm/, /ɪl/, /ɪr/. For example, "invisible".
"visible" becomes "invisible". It is a typical example of the in-/im-/il-/ir- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.