Let's say I call 'e' yellow. You say you know what I mean, and call 'f' green. But this makes no sense to me. Challenged, you claim to be doing the same thing I was doing. I smell a rat--are you making fun of me? Or just pretending to have understood what I meant? Or is it me that is missing some insight or imaginative discovery of yours? Or is something else going on? To what extent, or in what sense, can I accept that you are doing the same thing that I was doing if I don't at all share your view that 'f' is green?
It seems to me that we would have to have a conversation, and you would have to give me the kind of hints that people give when introducing someone to, say, a new kind of art. If I love Rothko or Pollock and you say that your five-year-old could have painted something as good, then I'll try to say and show you what I take to be so good about their work. You might get it, you might not. Much as if I were trying to teach my children to enjoy Shakespeare or philosophy. There isn't any fact we get to that shows it is good, like Wittgenstein's example of engineering in which there is a bridge that must not collapse. If the bridge supports traffic, it is a good bridge. There's nothing like that with philosophy (with, perhaps, rare exceptions when someone identifies an indisputable logical error) or literature or art. Or ethics. (Not that art is ethics. But the two are closer, at least in this regard, than either is to engineering considered in that kind of means-end, or meeting the objective/describable standard, way.)
Now what if you call suicide, as Chesterton does, "the ultimate and absolute evil" and I say that I know what you mean by "absolute evil" but disagree that the label is rightly applied to suicide? Perhaps I say that genocide is the ultimate and absolute evil. Are we talking past each other? It seems to me that we might be, but that only a conversation could make the answer clear. I don't mean that if we agree then by definition we are right in some sort of community-agreement-equals-truth kind of way. But if we agree that we did or did not mean the same thing by "absolute evil" then I don't see what grounds anyone else could have for saying we have got it wrong. Unless they join the conversation. Two uses are the same if they are like one another, and what is like what is a subjective (or inter-subjective) matter. Objectively, or as far as objectivity is concerned, everything is like everything else. So if saying that x is like y is going to have any point then there must be some relevant similarity. And relevance is (what I am calling) a subjective matter.
Which brings us to the question of (subjective) judgments of what things are like. What is the taste of pineapple? This. What is the taste of pineapple like? It's sweet. A bit like mango. A bit like apple.
"So you are saying that human agreement decides what is true and what is false?" -- It is what human beings say that is true and false; and they agree in the language they use. That is not agreement in opinions but in form of life.Compare this remark about opinions with this one: "I am not of the opinion that he has a soul." That other people have souls belongs to our form of life. Compare that remark about forms of life with this one: ""What has to be accepted, the given, is -- one could say -- forms of life."
There is no arguing about this, or no arguing other than the kind that goes on in relation to matters of taste. I cannot prove that green beans and raisins are horrible in the way I can prove that a collapsing bridge was badly designed or badly constructed. (I can, of course, prove whether people like them or not.)
It seems to me that Wittgenstein answers an important question ("So you are saying that human agreement decides what is true and what is false?") with a reference to "agreement in the language that human beings use" which could use some clarification. What is it to speak the same language? In a literal sense of "same language" two people might both speak, say, English. But not only is there another sense of "speaking the same language" that is less literal and less easy to identify, or impossible to identify objectively (I think I need to say more about what I mean by that), there is also a similar problem with regard to speaking English. That is, two people with little in common might be said not to speak the same language, even if both do in fact speak English. But even leaving aside that idiomatic use of "speak the same language" there are problem cases. Can a machine that passes the Turing Test speak English? At what point can a beginner be said to be able to speak English? When he can lie convincingly, as the Turing Test requires? When she can make a joke in English? When she dreams in English? Is American English the same language as British English? I don't think questions of relevance, and hence subjective judgments, can be completely avoided here.
And then there is another sense in which we can agree in the language we use. 'Language', like 'language-game', can refer to a part as well as the whole. It can mean wording. This might be a recent idiom, but it seems relevant to me. If "I feel absolutely safe" or "I wonder at the existence of the world" cannot be understood in a literal way, then how can we tell whether two people have the same feeling or wonder? How except by the words that they use to describe the feeling in question? And then it looks as though the two people's agreement in what they say decides whether it is true that they have the same feeling. Conclusion: I'm not sure that PI 241 is as straightforward as it seems.