C.S. Lewis on moral obligation

This semester I have the privilege of taking a seminar on moral obligation with C. Stephen Evans, who is currently working on a book arguing that the best account of moral obligation on offer is the Divine Command Theory of moral obligation. In our first class we discussed Elisabeth Anscombe's influential article "Modern Moral Philosophy" [found here online], which argued that without a divine lawgiver, we can't make good sense of the idea of moral obligation.

I'm also serving as a teaching assistant in a class on the thought of C.S. Lewis, and our first assigned book is The Problem of Pain (1940). Interestingly, in the first chapter Lewis makes a similar point to the one Anscombe made 18 years later:

All the human beings that history has heard of acknowledge some kind of morality; that is, they feel towards certain proposed actions the experiences expressed by the words 'I ought' or 'I ought not'. These experiences... cannot be logically deduced from the environment and physical experiences of the man who undergoes them. You can shuffle 'I want' and 'I am forced' and 'I shall be well advised' and 'I dare not' as long as you please without getting out of them the slightest hint of 'ought' and 'ought not'. [The Problem of Pain, (Harper Collins, 2001), p.10]