as though与seem在表面上看似有些相似，但实际含义和用法存在显著区别。

seem的结构主要包含三种形式：第一种为"It seems/seemed as if"或"It seems/seemed +形容词+that..."，表示仿佛或似乎。例如："At that time, it seemed as if I couldn't think of the right word anyhow." "当时,我似乎怎么也想不出一个恰当的字眼来。" 第二种为"人/动物/其他名词 + seem + to do"，表示某人或某物似乎在做某事。例如："The man seemed to be ill." "这个人好像病了。" 第三种为对第二种结构的简化，"seem +形容词"，表示某人或某物似乎具有某种性质。例如："He seems (to be) quite happy." "他似乎十分快乐。"

而as though表示仿佛、似乎，主要用来连接从句，描述一种假设或虚拟的情况。例如："It was as though the whole world was against him." "仿佛整个世界都在与他对立。"

综上，尽管seem和as though都表示某种推测或感觉，但seem用于陈述一种感觉或情况，而as though则用于描述一种假设或虚拟的状态。在使用时需要根据具体语境选择合适的表达方式。