Affect or effect? American speakers pronounce the two words identically, but their meanings are different.

When used as a verb, affect means "to change", and effect means "to make" or "to cause":

  • The desert heat affected the athlete's endurance.
  • The airplane effected a 180° turn before landing at the airport.

Sometimes usages are close:

  • The new legislation affected the price of fuel.
  • The new legislation effected a durable drop in fuel prices.

In the first case, the legislation was an influence, among others. In the second case, the legislation caused the change.

I received an e-mail alert last week from the New York Times, reporting that former vice-presidential candidate and Alaska governor Sarah Palin was resigning, "citing a desire to affect change outside of government". Minutes later, the online edition of the newspaper corrected the error and reported on Palin's desire to "effect positive change outside of government".

When used as a noun, effect means "a consequence", and affect (used rarely, usually in psychology) means "an emotion":

  • cause and effect
  • the patient showed no affect

Another noun form, affectation, means "putting on airs" or "acting in an artificial way":

  • an affectation of cleverness

When used as an adjective, effective means "to work":

  • medication must be proven safe and effective before it is offered to the public

A few other usages:

  • laws take effect or become effective on an effective date
  • personal effects are private belongings
  • special effects are used in movies to create an illusion