This paper is both systematic and historical in nature. From a historical viewpoint, I aim to show that to establish Wittgenstein’s claim that “an ‘inner process’ stands in need of outward criteria” there is an enthymeme in Wittgenstein’s private language argument overlooked in the literature, namely Wittgenstein’s suggestion that both perceptual and bodily experiences are _transparent_ in the relevant sense that one cannot point to a mental state and wonder “What is that?” From a systematic viewpoint, I aim to show (...) that Wittgenstein’s PLA teaches us that the prevailing picture of the nature of phenomenal concepts is upside down: we can only introspectively know what is going on inside our heads, after we learn of what is going on outside. In this regard, I aim to defend two associate claims against the prevailing view of PCs on the basis of PLA. First, by means of transparency, I aim to show that there is no _de re_ awareness of our private sensation that could determine the meaning of sensation-words; for example, I am never aware _of _the phenomenal blueness of my experience of something blue. The second associated claim is that introspective self-knowledge of our private sensation is always _de dicto_. We can only know introspectively that phenomenal blueness is the phenomenal character of the experience we are undergoing after we have learned _that _ blue is the color that usually causes in us that kind of experience. Likewise, we can only introspectively know that pain is the phenomenal character of the experience we are undergoing after we have learned that pain is what usually causes some typical pain behavior. (shrink)