It seems that he was right. 正确无误。其表达的意义为：现在看来他当时是对的。

至于这个that从句是什么从句，语法家也有争论。

第一种观点认为that从句是表语从句，但这无法解释it指什么。

第二种观点认为that是主语从句，it是形式主语。但却难以解释that从句为什么不能谓语句首，如：That he was right seems.

如果给seems后加个形容词，如obvious，

It seems obvious that he was rigght. 则that从句无疑为主语从句。

从《剑桥语法》提升主语结构的转换来看，似乎按照主语从句解释更为合理。试比较：

It is believed that he was right. （it为形式主语，that引导主语从句）

He is believed to have been right. （提升主语结构）

It seems that he was right. it为形式主语，that引导主语从句

He seems to have been right. (提升主语结构）

 It has turned out that he was right. 对

 It has turned out that he is right. 对

从句用过去时，是因为be right与现在无关。用现在时是因为be right在现在依然有效。