Propositional Attitudes

Knowledge is often taken to be a propositional attitude. Problems besetting epistemic modality appear to carry over to other kinds of modality based on propositional attitudes, such as doxastic modality (belief) and boulomaic modality (desire). E.g.

(Given everything Columbo believes) Joe must be the killer. (Given my desires for music) I must have that album.

Suppose we define doxastic necessity as following logically from a set of propositions believed by a subject, and doxastic possibility as compatibility with those beliefs. As with epistemic modality, all logical truths will turn out to be doxastically necessary. Yet, for a given logical truth p, I may believe neither hpi nor h¬pi, and my other beliefs may not rule out either. Surely hpi

and h¬pi both count intuitively as doxastically possible—for all I believe, p and for all I believe, ¬p—and yet one of them must be doxastically impossi- ble. The same goes for a notion of boulomaic modality, whereby boulomaic necessity is a matter of following from a set of desires, and boulomaic possi- bility a matter of compatibility with those desires. Again, logical truths will be boulomaically necessary. I may have no interest in whether hpi or h¬pi, and yet one will be boulomaically necessary. There is also the unwelcome consequence that logical falsehoods will be doxastically and boulomaically impossible, i.e. unbelievable and undesirable. But a bad logician may be- lieve a logical falsehood, and a long-suffering logician with an unwelcome end to his proof may desire that this logical falsehood be true. (And this is all without considering that we often have contradictory desires and beliefs.) Related problems arise for deontic modality. If we define deontic neces- sity as following from propositions comprising a moral code, say, then all logical truths will also follow from the moral code, and hence be deontically necessary. But it seems counter-intuitive to suppose that all logical truths ought to be the case, or must be the case in the sense of some moral im- perative. Indeed, one can imagine a strange moral code arising such that it is morally obligatory that some contradictions be true.18 Then it should follow from the moral code that some contradictions are true, but this has already been ruled out.

A possible diagnosis of these problems is suggested by highlighting the feature that these kinds of modalities, or at least doxastic, boulomaic and arguably epistemic, are based on a propositional attitude. Given a set of propositions to which an agent has a particular attitude, we can say how this bears on other, related propositions. E.g., if I believe that Torquay is in Devon, this has implications for the proposition that Torquay is not in Devon, i.e. given what I believe, it can’t be true. A pertinent question to ask here is: How far should modalities based upon our attitudes be expected to extend? Can we expect our having attitudes towards certain propositions to imply our having attitudes towards other propositions? If certain logi- cal truths and logical falsehoods do not fall under the purview of a set of propositions to which an attitude is held, nor propositions with a related content, perhaps we should be wary of extending the consequences of those attitudes to the unrelated propositions. It seems to me that this kind of sketchy diagnosis of the problems provides additional motivation for using a Relevant Logic. It seems to accord with the idea that having attitudes to- wards a certain set of propositions shouldn’t be taken to have consequences for our also taking attitudes to (relevantly) unrelated propositions.

The case of deontic modality is different, depending on one’s account of a moral code. If one takes the notions of right and wrong to be importantly connected to our attitudes, then all is well and good. If not, an alternative

diagnosis may be required. However, even if one doesn’t agree that deontic modalities have anything to do with propositional attitudes, one can still motivate the use of Relevant Logic to help solve its particular problems. Suppose we take a deontic modality to be based on some moral code, or suchlike. One would not expect matters falling outside of what is mentioned in that code to be bound by them. E.g., suppose I have a moral code consisting solely of the two following propositions:

1. Thou shalt not kill.

2. Honour thy father and mother.

A notion of deontic necessity relativized to these two propositions would render it impermissible (deontically impossible) for me to commit a murder. It would also make showing respect to my mother obligatory for me (de- ontically necessary). Deontic possibility, admittedly, could follow from the absence of any prescriptions, e.g., as this code does not mention stealing, it would appear to be permissible for me to steal something. What does seem counter-intuitive is that something should be impermissible or obligatory without it being explcitly related to something in the code. E.g., Classical tautologies such as if grass is green, then if the sky is blue then grass is green will be deontically necessary, but why must such a thing be so, in the sense of moral obligation? Have I been good if it’s true? Again, it seems that a neat way of out of this problem is to use a logic which requires premises to be relevant to a conclusion.