Assimilated Prefixes: When Prefixes Change Shape

Spot prefixes that changed their final letter to blend with the root, and use them to spell.

Some prefixes alter their last letter to match the sound that follows, a process called assimilation. It made words easier to say in Latin, and the spellings survived. The negative prefix in- becomes il- before l (illegal), im- before m, b, or p (immobile, imbalance, impossible), and ir- before r (irregular). The prefix ad-, 'to' or 'toward,' becomes ac- (accept), af- (affix), al- (allocate), and at- (attract). Com-, 'with,' becomes col- (collaborate), cor- (correspond), and con- (connect). Worked example: why does 'accommodate' have two c's and two m's?

It comes from ad + com + modus: the d of ad assimilated to c, and com kept its m before the m of modus. Spelling double letters becomes logical once you see the prefix underneath. Doubles at the seam are often a sign of an assimilated prefix.

• 1Assimilation changes a prefix's last letter to match the root.
• 2In- becomes il-, im-, or ir-; ad- becomes ac-, af-, al-, at-.
• 3Double letters at the seam often signal an assimilated prefix.