In this thesis I shall summarize and critically examine the central features of the theories of values of four contemporary moral philosophers: A.J. Ayer, C.L. Stevenson, R.M. Hare, and P.H. Nowell - Smith. I shall first look back, however, to the theory of moral philosophy of the most influential 'forefather' of this group, David Hume. Hume's theory stands as a challenge to moral philosophers who would assume that moral judgments are primarily, in some sense, acts of 'reason'. Although our four (...) contemporaries follow Hume in this, his challenge, in the form I shall indicate shortly, will provide the main theme for this thesis. (shrink)