这个问题首先要了解以下几个方面：
A.seem 后面是接不定式的,也可以接形容词.
e.g.That seems very easy.(形容词）
e.g.He seems to have known it already.(不定式）
B.不定式属于非谓语动词.凡是非谓语动词,其否定式,not 或其它表示否定的词 如never
hardly 等,都位于非谓语动词的前面
e.g not to know,not knowing,not having been told 等等,总之,非谓语动词的否定,
其否定词都位于其前面.
e.g.He pretended not to know her and passed away.他假装不认识她.