Perhaps you should try some spelling variations:
"effective theory" » "effect theory", "effective tool", "effective team"
"affect theory" » "effect theory", "effects theory"
"act theory" » "art theory", "exact theory", "action theory"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("affect theory") OR ("effective theory"))) OR ("act theory")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"affect theory\") OR (\"effective theory\"))) or (\"act theory\"))".
• Removing quotes may allow a broader search: (((( affect theory ) OR ( effective theory ))) or ( act theory )).
• Adding a wildcard symbol may retrieve word variants: (((("affect theory") OR ("effective theory"))) or ("act theory"))*.