Wittgenstein’s axiom that “what can be said at all can be said clearly” is frequently quoted, but much of the Tractatus is dedicated to Wittgenstein explaining how what is said at all is said in pictures. To the extent that this philosophy is the heart of modern analytic thought, such thought has the same root as the old Empirical school: reduce all knowledge to sensation, and understand sensation primarily, if not entirely, through vision.
The reduction of all sensation to pictures happens very easily. As Augustine points out, we use the act of sight analogously to speak of the clarity we have in the other senses: e.g. “see how this tastes” or “I see what you’re saying”. But while vision has the benefit of being the clearest sense, it most obscures the nature of sensation itself. When we understand all sensation through vision, we easily fall into thinking that sensation is nothing but a picture. The obvious problem with this is that if sensation is nothing but a picture, then pictures would see. Said another way, to call vision a picture explains everything- except the very act of vision we were trying to explain in the first place. This “little picture” theory never comes up if one remembers that touch and taste are sensations too: is touching a “little touch”? Of course not. Again, even it it were a little touch, it would not explain why we feel it.
Another difficulty with understanding all sensation though sight is that while sight excells all other senses in making distinction known, it does not excell all senses in every way. Hearing surpasses sight as a sense of learning, because we learn most perfectly though words, and words are, properly speaking, things said. Touch surpasses all senses in establishing existence- think of the request of the Doubting Thomas.
One can construct various artifacts to represent the various sensations in picture: Wittgenstein himself says that the notes on a scale are a picture of music; and I suppose he could also say that the rising of the mercury is a picture of heat, or a lemon is a picture of the sour, etc. In doing this, however, we lose the unity of the sense experience- music and noise are one as audible, sweet and sour are one as tastable. But more importantly (again) by explaining hearing though sight we haven’t explained something as heard, and in some sense we do not need to. Sounds and smells and tangible experinces are known in themselves, and have certitude in themselves. They do not stand in need of some pictoral representation to make them understood or certain.