We have been considering various attempts to give an account of knowing of the following form:
Necessarily: For all s and p: s knows p iff (a) p is true, (b) s believes p, and (c) ...
Williamson, T. (2000), Knowledge and its Limits (Oxford: OUP), pp. 2-5, 27-33, calls into question whether or not this can be done. The way I read Williamson, he considers four reasons to think that it can be done, and argues against each. And he gives two reasons to think that it cannot be done.
Read the relevant sections of Williamson. What reasons for thinking that it can be done does he consider, and what does he say against them? What reasons does he give for thinking that it cannot be done?