Imperatives cannot be true or false, so they are shunned by logicians. And yet imperatives can be combined by logical connectives: "kiss me and hug me" is the conjunction of "kiss me" with "hug me". This example may suggest that declarative and imperative logic are isomorphic: just as the conjunction of two declaratives is true exactly if both conjuncts are true, the conjunction of two imperatives is satisfied exactly if both conjuncts are satisfied—what more is there to say? Much more, (...) I argue. "If you love me, kiss me", a conditional imperative, mixes a declarative antecedent ("you love me") with an imperative consequent ("kiss me"); it is satisfied if you love and kiss me, violated if you love but don't kiss me, and avoided if you don't love me. So we need a logic of three -valued imperatives which mixes declaratives with imperatives. I develop such a logic. (shrink)

Besides pure declarative arguments, whose premises and conclusions are declaratives (“you sinned shamelessly; so you sinned”), and pure imperative arguments, whose premises and conclusions are imperatives (“repent quickly; so repent”), there are mixed-premise arguments, whose premises include both imperatives and declaratives (“if you sinned, repent; you sinned; so repent”), and cross-species arguments, whose premises are declaratives and whose conclusions are imperatives (“you must repent; so repent”) or vice versa (“repent; so you can repent”). I propose a general definition of argument (...) validity: an argument is valid exactly if, necessarily, every fact that sustains its premises also sustains its conclusion, where a fact sustains an imperative exactly if it favors the satisfaction over the violation of the imperative, and a fact sustains a declarative exactly if, necessarily, the declarative is true if the fact exists. I argue that this definition yields as special cases the standard definition of validity for pure declarative arguments and my previously defended definition of validity for pure imperative arguments, and that it yields intuitively acceptable results for mixed-premise and cross-species arguments. (shrink)

Besides pure declarative arguments, whose premises and conclusions are declaratives, and pure imperative arguments, whose premises and conclusions are imperatives, there are mixed-premise arguments, whose premises include both imperatives and declaratives, and cross-species arguments, whose premises are declaratives and whose conclusions are imperatives or vice versa. I propose a general definition of argument validity: an argument is valid exactly if, necessarily, every fact that sustains its premises also sustains its conclusion, where a fact sustains an imperative exactly if it favors (...) the satisfaction over the violation proposition of the imperative, and a fact sustains a declarative exactly if, necessarily, the declarative is true if the fact exists. I argue that this definition yields as special cases the standard definition of validity for pure declarative arguments and my previously defended definition of validity for pure imperative arguments, and that it yields intuitively acceptable results for mixed-premise and cross-species arguments. (shrink)

My dissertation addresses the question "do desires provide reasons?" I present two independent lines of argument in support of the conclusion that they do not. The first line of argument emerges from the way I circumscribe the concept of a desire. Complications aside, I conceive of a desire as a member of a family of attitudes that have imperative content, understood as content that displays doability-conditions rather than truth-conditions. Moreover, I hold that an attitude may provide reasons only if it (...) has truth-evaluable content. Insofar as desires lack truth-evaluable content, I hold that the content of a desire has the wrong kind of logical structure to provide reasons. My second line of argument claims that even if a desire did have truth-evaluable content, it would not follow that desires provide reasons. This is because a desire has no more rational significance than a guess or coin-flip. My argument relies on what I call the non-substitutability principle, the thesis that (all things being equal) one cannot substitute something that lacks rational significance, relative to some attitude, A, for something that has rational significance, relative to A, and leave the rational standing of A unchanged. For example, one cannot substitute the guess that P (i.e., something that lacks rational significance relative to the belief that P) for the perception that P (i.e., something that is rationally significant relative to the belief that P) without altering the rational standing of the belief. I argue that when the non-substitutability principle is applied to a desire that gives rise to an intention, it turns out that one can always substitute a guess or coin-flip (i.e., something that lacks rational significance relative to the intention) for the desire, without altering the rational standing of the intention. I take this to show that desires are not rationally significant relative to the intentions to which they give. (shrink)