As he [Wittgenstein] puts it in the book’s [Tractatus Logico-Philosophicus] preface: “The aim of the book is to draw a limit to thought, or rather – not to thought, but to the expression of thoughts: for in order to able to draw a limit to thought, we should have to find both sides of the limit thinkable (ie we should have to be able to think what cannot be thought).”
But, just as we cannot think what cannot be thought, so we cannot say what cannot be said. Wittgenstein acknowledges that this means that his own sentences are themselves meaningless. “My propositions,” he wrote, “serve as elucidations in the following way: anyone who understands me eventually recognises them as nonsensical, when he has used them – as steps – to climb up beyond them. (He must, so to speak, throw away the ladder after he has climbed up it.)
”That “ladder” is a theory of language called the “picture theory of meaning”. Every meaningful proposition, Wittgenstein maintains, pictures a possible state of affairs in the world, and is either true or false depending on whether that state of affairs does or does not obtain in the world. Thus, “My shirt is red” is meaningful because the state of affairs it pictures is at least possible, and it is, as it turns out, true. On the other hand, “My shirt is blue” is meaningful but false. “God is great” is neither true nor false because it lacks meaning; it does not picture a possible state of affairs in the world.
The same is true of Wittgenstein’s own propositions expressing this theory. They do not picture possible states of affairs in the world and therefore lack meaning, which is why they must be discarded.
Nevertheless, the logical and linguistic truths they show are, as he puts it, “unassailable and definitive”. What enables us to show truths about logic and language is what Wittgenstein calls “logical form”, which he likens to pictorial form. In order for a painting or photograph to represent a scene, it must have something in common with it. That something is pictorial form. A painting can picture, say, a hay wain, but it cannot picture the pictorial form that allows it to do so. Likewise, a sentence can say something true about the hay wain, but it cannot say anything about the logical form that enables it to do so.
The picture theory of meaning has had an enormous influence on the development of philosophy. Its influence began in Vienna, where it inspired the logical positivists to advance their own “verification principle”, which declared that any proposition that could not be verified as true or false was meaningless, and soon spread to Cambridge and then Oxford, where it shaped the analytical tradition, which came to dominate English-speaking philosophy. The remarks in the Tractatus about God, religion, ethics, aesthetics and the meaning of life have had little influence within analytical philosophy but have intrigued a wide variety of creative people.