X’不可見性原則」聲稱片語結構的中間層級是不可參與句法計算的(主要參考Chomsky 1995)，支持這個原則的證據來自於X’組詞成分不允許句法移位、省略也不能被用來當作不完整句。在本篇文章中，我認為這樣的原則在概念上和經驗上皆是有問題的。我主張句法移位的限制可以用「擴張和鏈鎖一致性」輕易地說明，而省略和不完整句的限制則可以用選擇特徵和句法投射的本質來解釋。

The X’ Invisibility Principle claims that intermediate (X’) levels of phrase structure are unavailable for syntactic computation (see especially Chomsky 1995). Evidence for this principle comes from the fact that X’ constituents resist operations such as movement and ellipsis and cannot be used as segment fragments. In this paper I argue that this principle is problematic on both conceptual and empirical grounds. I claim that movement restrictions are readily accounted for by Extension and Chain Uniformity, while restrictions on ellipsis and sentence fragments can be explained in terms of selectional features and the nature of syntactic projections.