In the New Statesman, Ray Monk looks at Wittgenstein's visual thinking.

It was fundamental to Wittgenstein’s thinking – both in his early work Tractatus Logico-Philosophicus and in his later work Philosophical Investigations – that not everything we can see and therefore not everything we can mentally grasp can be put into words. In the Tractatus, this appears as the distinction between what can be said and what has to be shown. “Whereof one cannot speak, thereof one must be silent,” runs the famed last sentence of the book but, as Wittgenstein made clear in private conversation and correspondence, he believed those things about which we have to be silent to be the most important.

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Wittgenstein suggests we understand words as picking out not some single thing but a group of things that need not have anything in common. Rather, like members of the same family, they might have a series of similarities and dissimilarities that overlap and criss-cross in various complicated ways. Some Wittgensteins (such as Ludwig and his sisters) might have the same nose, the same mouth, the same eyes but, say, different foreheads. There need not be one thing that all members of the family have in common. Likewise, there need not be any one thing that all instances of the word “truth” have in common. The philosophical task of looking for the essence of truth, then, is unending, not because it is deep but because it is an example of the ways in which we can be captured by a picture.

I'm finishing Susan Sterrett's Wittgenstein Flies a Kite , in which she argues that Wittgenstein's insight in the Trac derives from his study of Edgar Buckingham's π theorem of dimensionless analysis. That thinking through the dimensionless relationship between physical variables (e.g., the Reynolds number in fluid mechanics), can provide an understanding of problems that are not solvable using only logical propositions or dialectics.