Among other things, Wittgenstein takes on a foundationalist (and to some extent a verificationist) epistemological system; instead he offers a coherence model of epistemology. I.e., we have a system of beliefs (I may want here to say knowledge, there's a distinction that remains perfectly unclear [not perfectly clear] to me), but that system is ultimately non-grounded. The axis of my system is immoble, "but the movement around it determines its immobility" (152).
The difficulty is to realize the groundlessness of our believing. (166)Fine. But how do we know to act morally? Wittgenstein's epistemic stance has to do with our whole system of beliefs, which is not (necessarily not) grounded. The foundation of the house is, so to speak, held up by the walls (248). This epistemic stance is not outrageous; I think it was advocated in my phil335 epistemology class.
If true is what is grounded, then the ground is not true, nor yet false. (205)
All this talk is just to spin the tires, though: One could disagree, but I think (and I think this is what Wittgenstein means) along with Wittgenstein that the real juicy problems are the problems that actually occur. "Our talk gets its meaning from the rest of our proceedings" (229). Along the same lines, knowledge is not a mental process or state of mind--knowledge seems to be derived after the fact. Intention, as well. Justifications (epistemic) are means toward an end, which is action. Our action ultimately shows our knowledge and our justifications.
What would it mean to say, 'I should not kill'? If I had more inclination, I would write about riding bikes.
You don't know how to ride a bike at all times. (Given, that is, you ever knew how to ride a bike.) Times when you ride a bike and times when you say, 'I know how to ride a bike' are when you know how to ride a bike. If you're not thinking about bike riding, do you know how to ride a bike? How? How can you know it if you don't know it? When don't you know?
When I say 'I shouldn't kill' it only makes sense if I'm feeling a temptation to kill. My actions continuously demonstrate this moral imperative. How is this different than knowing how to ride a bike?