Business Writing Center
Affect/Effect:
The word effect is usually a noun, as in the phrase “cause and effect.”
Example: The effect of her decision to network the computers was better communication among team members.
The word affect is usually a verb.
Example: The attitude of management affects employee morale at all levels.
Occasionally effect is used as a verb that means, "to cause." Effect used as a verb carries with it the connotation of completeness, of having done something to the full.
Example: She effected a complete turnaround in productivity by streamlining the system process.
As/Since
Though British writers generally use as and since interchangeably, American writers distinguish between them. As used as a conjunction connotes a contemporary time, something happening while something else is happening.
Example: They turned on their laptops as the flight took off.
Since gives a sense of something happening in consequence of something else.
Example: The flight attendant chastised the passengers using laptops since no electronic devices could be used until ten minutes into the flight.
A While/Awhile
Awhile is an adverb used to modify verbs.
Example: He stayed awhile.
While is a noun expressing an unspecified but usually short period of time. It is often the object of a preposition.
Example: He stayed for a while.
Generally, use awhile in the absence of a preposition, and a while following a preposition.
That/Which
Use that to introduce restrictive clauses, and use which to introduce nonrestrictive clauses. Restrictive clauses add essential information to the core statement of the sentence; nonrestrictive clauses add information that may be parenthetical, interesting, and valuable but not essential to the meaning the writer is trying to convey. You cannot leave a restrictive clause out and preserve the meaning of the sentence; however, you may omit a nonrestrictive clause without damaging the meaning of the sentence.
Example of restrictive clause: Of all my teachers, the one that taught negotiation was the best. If you remove the restrictive clause, "that taught negotiation," the sentence makes no sense.
Example of nonrestrictive clause: My economics professor, whom I just saw at Caribou, was the most informative. The sentence conveys its intended message without, "who I just saw at Caribou."
Adapted from Richard Marius's A Writer's Companion with additional examples by Ann Campbell.