From VOA Special English:
Germany is facing a crisis as low birth rates combine with a growing population of citizens who are living longer.
The word "combine" somehow confused me. In my view, we can use the expression "combine with" in the following forms:
<somebody> combine <something> with <something>
<something> is combined with <something>.
Of course, "low birth rates" and "a growing population of citizens" both belong to "<something>", and considering the omitted verb "is", I think maybe "combined with" is more appropriate. So, can anyone tell me why does it use "combine" instead of "combined"?
Best Answer
Like many verbs of conjunction or concoction like mix, join, merge, blend, and so on, the subject of combine can either be the person or thing initiating the combination or one of the constituents being combined. Your second usage is perfectly acceptable in the active voice, i.e. <something> combines with <something>, as it is with the other verbs:
Combine is appropriate in the VOA quote. It is the main verb of the sentence, indicating that rates are combining with population. Combined with would be ungrammatical; the dependent clause introduced by as would have no main verb because combined would be a participle.