Foreigners often make some strange mistakes in Chinese when they study the most difficult language--- ---Chinese. We try to analyze typical sentences to correct these errors.

          Wǒmen ɡēn tā kéyǐ tánhuà le.
False: 我们跟他可以谈话了。
          Wǒmen kéyǐ ɡēn tā tánhuà le.
True: 我们可以跟他谈话了。

介宾词组(“跟他”)和能源动词(“可以”)出现在同一动词之前,它们的排列顺序是:介宾词组靠近动词,其次是能源动词,应把“跟他”放在“可以”的后头。
Where a prepositional phrase(跟他) and an auxiliary verb(可以)occur simultaneously before the same verb, the order is: the prepositional phrase immediately precedes the verb, and the auxiliary verb goes before the prepositional phrase. One should place 跟他 after 可以.