Assimilated Prefixes: When IN- Becomes IM-, IL-, IR-

Recognize prefixes that change spelling to match the next letter, like in- to im-, il-, ir-.

Some prefixes change their last letter to blend with the root that follows. This is called assimilation, and it explains many doubled letters. The prefix in- meaning 'not' becomes im- before b, m, and p: immature, impossible, imbalance. It becomes il- before l: illegal, illogical. It becomes ir- before r: irregular, irresponsible. The meaning never changes; only the spelling does, because the new spelling is easier to say. Other prefixes do this too. Ad- (to, toward) becomes at- in attract and ac- in accept.

Con- (together) becomes col- in collect and com- in combine. This is why 'illegible' has two l's: il- plus legible. Here is how it helps when reading: 'The handwriting was illegible. ' Spot il- as a disguised 'not', recall 'legible' means readable, and you know the writing could not be read. Doubled letters at the start of a word often signal a hidden prefix.

• 1IN- (not) changes to IM-, IL-, or IR- to match the next sound.
• 2The meaning stays the same when the spelling changes.
• 3Doubled letters at the start often mark a hidden prefix.