The phrase 'combine theories' is correct and usable in written English.
You can use it when you want to describe the process of putting two or more theories together to make a new one. For example, "The researcher combined several theories to create a new holistic approach to the problem."
They have managed to combine theories about ethics and metaphysics with practical involvement in a range of interests – education, fashion, politics, travel, publishing, art and architecture – which puts to shame the scope of the achievements of even the greatest secular movements and individuals in history.
In addition, the paper tries to combine theories and perspectives from a multi-disciplinary research of demography, organizational sociology, and social psychology.
To better understand these relationships between eye movements and comprehension during film viewing, further studies need to combine theories and methods from the fields of scene perception, event perception, and narrative comprehension (Loschky, Hutson, Magliano, Larson, & Smith, 2016; Loschky, Hutson, Magliano, Larson, & Smith, 2014; Magliano, Larson, Higgs, & Loschky, 2016).
In this way, one can combine theories even if component theories use different vocabulary for the same concept, or the same vocabulary for different concepts.
Contributions the judiciously combine theory and experiments are highly encouraged.
The ability to combine theory, creativity and engineering was a great achievement of postwar America.
Students combine theory with case studies to find solutions to everyday problems.
All programs within the College combine theory with application to foster creative problem solving skills.
Chicago Price Theory, the university's special contribution to economics, aims to combine theory and data in the face of a growing disconnect in academia.
The classes combine theory with the real world, and allow you to quantify what is otherwise seen as qualitative.
The degree allows graduates to combine theory with practice, gaining hands-on experience through industry placements as well as learning about areas such as finance, marketing, management theory, human resources, food science and nutrition.
