本文解釋、並評論了從1940 年代至1970 年代中幾個重要的、有關於虛擬條件句的理論。這些包括可共同性支撐理論、嚴格條件句理論、世界選擇語意論、集合選擇語意論、與範圍語意論。我駁斥了可共同性支撐理論、嚴格條件句理論與世界選擇語意論，同時論證說，某種形式的集合選擇語意論或範圍語意論是到目前為止最為合理的理論。連帶地，我論證說，VW 系統是到目前為止最合理的虛擬條件句邏輯系統。在本文的餘論中，我進一步指出了這些語意論在科學哲學、小說討論、與確定描述詞理論中的可能應用。

This paper explains and comments on the most important theories of subjunctive conditionals from 1940s to 1970s. These include cotenability theory, strict conditional theory, world selection semantics, class selection semantics and sphere semantics. I refute cotenability theory, strict conditional theory and world selection semantics as inadequate, while argue that some versions of class selection semantics or sphere semantics are the best semantic theories among all that we have seen for subjunctive conditionals. Accordingly, I also argue that Lewis’s VW is the most satisfactory logic system for subjunctive conditionals among all the systems we have checked. In the final part of the paper, I point out some applications of these semantic theory to fiction discourse, definite descriptions and topics in philosophy of science.