believes是一般现在时,has convinced是现在完成时,都是属于现在时,与你所讲的标准并无冲突。不过not only...but also实际使用中也不一定是这样时态一致的,要看具体情况。例如:He speaks very good English because he not only works in a Brtish company but he actually stayed in the USA for ten years when he was a kid. (他的英文很流利,不仅因为他现在在一家英国公司工作,还因为他小时候实际上在美国呆了十年。)