This is a much-discussed aphorism (Philosophical Investigations II 190), and even now Wittgenstein scholars differ over how it should be interpreted. But everyone can agree that its meaning depends crucially on what Wittgenstein means by understanding (verstehen).
Here’s what he says about that in Philosophical Investigations §§531–532:
We speak of understanding a sentence in the sense in which it can be replaced by another which says the same; but also in the sense in which it cannot be replaced by any other. (Any more than one musical theme can be replaced by another.)
In the one case the thought in the sentence is something common to different sentences; in the other, something that is expressed only by these words in these positions.
Then has “understanding” two different meanings here? – I would rather say that these kinds of use of “understanding” make up its meaning, make up my concept of understanding.
For I want to apply the word “understanding” to all this.
At one level, understanding means grasping the general meaning of an expression. At this level, “I’m going to walk the dog” and “I’m going to take the dog for a walk” mean the same thing. If you heard someone (call her Alice) use either expression under the right circumstances, you’d be justified in forming the expectation that she would soon walk the dog. You’ll have understood her well enough to predict her behavior.
But you would not have understood her as a unique individual, which is what I take to be the second level of understanding.
At the second level, taking the dog for a walk has a meaning that is unique to Alice. Her attitude towards her dog (call him Boxer), the role walking him plays in her life, the impact on her of the weather that day, the route she plans to take, and much more, pertain to her alone.
To understand her on this level, you must understand (a) what walking Boxer means to Alice and (b) how Alice’s word choice and expression convey that meaning on this particular occasion. You would understand, even if only implicitly, that Alice did not say “It’s time to walk the dog,” which would have conveyed (to you, because you know Alice well) that she wasn’t looking forward to it – perhaps because of the weather or because her route takes her past the house of a neighbor with whom she’d been quarreling. You would know that “the dog” is a term of affection for Alice, and did not suggest an impersonal relationship with Boxer – as someone who understood her only at the first level might not unreasonably presume.
The point is that although walking Boxer is something that Alice does every day, it’s always possible on any given day that performing this routine will mean something a bit different from what it meant the day before, and that Alice will express that difference in ways that are unique to her.
If a lion could talk at all, we would certainly be able to understand him in some sense. We would understand that he desired to communicate or express himself in some way. As fellow-mammals, we have enough in common with lions to infer beliefs and desires from their behavior, and we could presumably learn at least some of his language by correlating actions with expressions.
So we shouldn’t take Wittgenstein as saying that we couldn’t understand a talking lion at the first level of understanding. But Wittgenstein says he means both levels – “all this” – when he talks about understanding. Presumably, it’s the second level that Wittgenstein has in mind: we couldn’t understand the lion as a unique individual.
Why not? The answer must be, I think, because we can’t enter into a personal relationship with a lion. To grasp what Alice means when she expresses an intention to walk the dog requires that we know an awful lot about her experiences, memories, concerns – about what matters to her. When Alice says she’s going to walk the dog, she’s saying it in a certain manner (excited, resigned, weary, fearful, matter-of-factly) and with a certain facial expression (happy, contented, determined, grim), which help make it possible to understand her at the second level.
None of this is available in the case of a lion, not even a talking one. For purely physical and biological reasons, our world and the world of the lion’s overlap to an extent. But they don’t overlap sufficiently for humans and lions to be able to get to know one another personally.
If this is right, Wittgenstein’s meaning could be expressed by saying that if a lion could talk, we could understand him, but we couldn’t fathom him. We couldn’t “get” a talking lion the way we “get” Alice. We could understand him in a general way, but we could never take him in.
In Wittgenstein’s terms, we could not “find our feet” with him. Imagining a group of human beings who never express their feelings, Wittgenstein considers this reaction:
“These men would have nothing human about them.”
Why? – We could not possibly make ourselves understood to them. Not even as we can to a dog. We could not find our feet with them.
And yet there surely could be such beings, who in other respects are human. (Zettel §390.)
If a lion could talk, we could understand him, in a general way, but we could not find our feet with him.
Now, what’s the point of Wittgenstein’s observation? It goes back to the idea that words have meaning (i.e., use) in the context of a “form of life.” Going beyond the letter of Wittgenstein, I’d say that the human form of life is person-to-person. In Martin Buber’s terms, we are in I-You relationships not I-it relationships – at least until something goes wrong.