A vs. An with Acronyms. Use a or an based on the acronym's pronunciation. Grammar Some of the most common writing mistakes involve these tricky grammatical rules. Affect vs. Effect. Affect is a verb that means to influence .
Effect is a noun that means a result .
If you affect something, you can cause an effect. That vs. Which. This is a toughie, and even editors don't always agree. The web site, which Catherine uploaded to the server, crashed when we looked at it. The web site that Catherine uploaded to the server crashed when we looked at it.