Perhaps you should try some spelling variations:
"observations theory" » "observations thereon", "observations towards"
"generative theory" » "generalized theory", "integrative theory", "alternative theory"
"generation third" » "generation theory", "generation theorem", "interaction third"

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: (((("generation third") OR ("observations theory"))) OR ("generative theory")).
• Removing quotes may allow a broader search: (((( generation third ) or ( observations theory ))) or ( generative theory )).
• Adding a wildcard symbol may retrieve word variants: (((("generation third") or ("observations theory"))) or ("generative theory"))*.