Prefix · formal negation
Formal Latin-origin negation with four phonetic forms: invisible, impossible, illegal, irregular.
Written by Bryan López, English teacher · Updated
In- has four phonetic variants determined by the first letter of the root: im- before "p" or "b" (impossible, imbalance), il- before "l" (illegal, illogical), ir- before "r" (irregular, irresponsible), and in- everywhere else (invisible, incorrect, inactive). The meaning is always "not" or "without." The variants exist purely to make pronunciation easier.
English has two negation systems: in- (and its variants) attaches to Latin or French-origin words (invisible, incorrect, impossible), while un- attaches to Germanic-origin words (unhappy, unkind, unfair). A practical rule: if the root ends in "-ible/-able/-ive/-al," it usually prefers in-.
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
Learn the variants as a sound pattern: "im-" before p/b (impossible, imbalance), "il-" before l (illegal), "ir-" before r (irregular), "in-" everywhere else. Say the words aloud and the variants will feel natural.
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. In Spanish it usually maps to in- / im- / il- / ir-.
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.