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Multiculturalism has gained the status of a general theory, complementing other scientific theories to explain human behavior.

About the infinitive 'to explain', does it refer to 'other scientific theories' (i.e modifying the noun in front), or 'complementing' (i.e.working as an adjective).
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I hope I understand the point of your question, Taka.

I read the intent this way:

Multiculturalism, recently elevated to the status of a general theory, complements other theories that already exist as explanations of human behavior.
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Yes; it looks as if 'that explain' was the intended meaning.

MrP
OK.

Thank you, people!