Those who have taken up this expressivist program have provided a number of candidates for the attitudes expressed by sentences containing normative terminology.  Simon Blackburn, whose quasi-realist project was briefly described above, has contributed various ideas not only for the states expressed by indicative sentences but also for complex embeddings of moral claims.  Hybrid theories that put the expressive function of normative language into the semantics (discussed below) also involve work of this sort. But the proponent who has developed the program in the most systematic way is Allan Gibbard. In two influential books Gibbard has proposed two structurally similar accounts each of which employs a different base noncognitive attitude.  In Gibbard (1990) the attitude was norm-acceptance, whereas in Gibbard (2003) it was a planning attitude akin to intending.  In each case he develops a strategy for combining the relevant noncognitive attitude with belief to generate complex attitudes  that can serve as the semantic values of more complex sentences.  Mark Schroeder’s (2008c) bifurcated attitude semantics is a self-conscious attempt to develop these strategies yet further and to assess prospects for the general strategy.