Wittgenstein said that when we call something senseless it is not as it were its sense that is senseless, but a form of words is being excluded from the language.
The 'exclusion from the language' is done not by legislation but by persuasion.
If we say 'it does not make sense for this man to say he did this for no particular reason' we are not 'excluding a form of words from the language'; we are saying 'we cannot understand such a man'. (Wittgenstein seems to have moved from an interest in the first sort of 'not making sense' to the second as Philosophical Investigations developed.)
There is not, it seems to me, a very sharp line between not understanding a man on account of what he says and not understanding a man on account of what he does. I don't mean there is no difference at all, necessarily, but the cases are surely closely related.
Later in the book Anscombe suggests that the question 'Why?', as in 'Why are you doing that?', amounts to asking 'What's the good of that?' And here, she says, "the good (perhaps falsely) conceived by the agent to characterise the thing must really be one of the many forms of good." (pp. 76-77).
When we cannot understand a man's doing this or that it seems that we cannot see the (supposed) good in what he is doing. If he kills someone to get his money then this makes sense, we can see why getting money seems (or is) good. But it only makes sense up to a point, it seems to me, given that we can still wonder about the goodness or sense of killing someone in order to get their money. If I met a mercenary, for instance, I might understand easily enough that he kills people because of the money, but I still might be quite mystified as to how he can see that as an acceptable way to make money. My understanding only goes so far. Another mercenary might understand better, but different mercenaries might draw the line in different places. I had a friend in high school with an unhealthy interest in mercenaries. He told me that it was common for people to advertise their services in Soldier of Fortune magazine with the line 'Any cause but red,' meaning they will fight for anyone except communists. That kind of mercenary might not understand one who was prepared to fight for any cause at all.
The ways we live allow for certain possibilities and rule others out, or our lives are defined (at least in part) by what they exclude as possibilities. I could be an atheist or a Catholic or a Buddhist, but Shinto is not really an option for me, and the way of the samurai is definitely out. This says something about how I live and who I am. Certain forms of behavior and belief are excluded from the possibilities for my life. Not by my ethics, but by something that surely relates to ethics. It has, after all, to do with what I can make sense of as good.
Over at The Limits of Language I've written the following in the comments:
Given how we live with other human beings, throwing dead (and dying!) people to be eaten by pigs might be a kind of contradiction. Soldiers returning from war often have a hard time adjusting to normal life because of this kind of contradiction between how they acted during the war and how they must act now that they are out of the war. This might be taken as a reason for thinking that the things one only would do in a war should never be done. Alternatively it could be taken as a sign that they are wrong. Whether it is a reason or a sign or neither is a tricky question, I think. (As is what it would mean to call it a sign.)I think the key idea here is reasonableness. However narrowly rational evil acts might be, they are not reasonable. But do I want to make reasonableness the standard of moral goodness? That doesn't sound right.
Not everything that leads to psychological problems later in life is necessarily wrong though. Say a soldier is fired on by a thirteen year-old boy, and fires back, killing the boy. Was this wrong? Not obviously. But I can imagine it might be very hard to live with having done something like that. So I'm reluctant to say that every act that is hard to live with must be wrong. Perhaps it is, but I'm not ready to draw that conclusion. On the other hand, an action's being hard to live with seems to be at least prima facie reason for thinking there is something bad about it. And not just its effect on one's mental health. It seems to be its badness, perhaps its disjointedness in relation to the rest of our lives, that makes it bad for our mental health.
This makes me think of Cora Diamond's work on problems of life. But I also have in mind Wittgenstein's saying in Investigations 500 that, "When a sentence is called senseless, it is not as it were its sense that is senseless. But a combination of words is being excluded from the language, withdrawn from circulation." Certain ways of treating human beings and their bodies are excluded from the dictionary of acceptable forms of behavior. They are not in circulation. And when someone tries to introduce them they are rejected. Not because they are inherently worthless/senseless/impossible to circulate. But because they don't fit well with the pre-existing economy.
Something like this, at least, is the kind of thinking I want to explore.