Think about the term cause and effect when picking between affect and effect.
They are out there lurking around, waiting to embarrass you when you're writing for an audience. They are commonly misused words. Words like to, two and too or altogether and all together are some of the examples of words commonly misused when writing. Another example of commonly misused words is effect and affect. Typically, confusion occurs because affect and effect are homonyms: words that sound similar, but have totally different meanings.
Effect Definition
Effect, generally used as a noun, infers the result, cause or agent. Thus, you'd use effect when you're talking about an outcome or something caused by something else. If you were discussing new management you may write: "It's interesting to see the effects the new rules produce."
Affect Definition and Usage
The word "affect" means to influence. Typically, you should use affect as a verb: "His speech affected me on an emotional level." Use affect as a noun when describing facial expressions: "Eddie had a sad affect."
Using Effect as a Verb
There is an instance where you use effect as a verb -- when you're writing about something produced or change brought about. If you want to talk about a new boss making positive changes in your work environment you'd write: "Dave, the new manager, effected some positive changes in my office." Using effect in this way shows the changes brought about by the new manager."
Use in Psychology
Use affect when you're discussing something or someone's influence - rather than causing the change. If you're writing a psychology paper, you generally use affect as a noun. Psychologists use "affect" instead of "effect" as a noun because they can't positively know how patients feel - they can only see how they appear.
