Friday, February 08, 2008

Dimensions of Desire

Following Alonzo Fyfe, I once accepted the following thesis:
(BDI) People always act so as to fulfill their most and strongest desires, given their beliefs.

But this is either trivial or false.

It is trivial if we weight desires according to their eventual behavioural impact, so that BDI stipulatively defines 'desire'. But this is rather pointless, since it means that we cannot tell what desires someone has until we see which act they perform. (And if their decision is highly sensitive to trivial situational changes, as seems likely, then desires would seem not to have any stable prior existence.) So it seems like a bad definition. In any case, interesting truths cannot be arrived at by mere stipulation.

If we want BDI to be a substantive thesis, it must invoke some independent notion of desire (strength). The most obvious contender here is the felt strength of a desire in our conscious phenomenology. But then BDI is simply false: we are not always bound to follow that which most tempts us -- the will may override mere feelings.

Finally, there is the (more morally important) dimension of reflective endorsement, where we may more naturally speak of 'ends' than 'desires'. But again, this interpretation renders BDI false: unfortunately, we do not always pursue those ends we believe to be best. We may be waylaid by mere (unendorsed) desires.

This distinction is captured rather nicely in Sidgwick's Methods of Ethics (1890). The suggestion that "adoption of an end means the preponderance of a desire for it" - precluding the possibility of instrumental irrationality - is due, he suggests, to "a defective psychological analysis" (p.39):
According to my observation of consciousness, the adoption of an end as paramount -- either absolutely or within certain limits -- is quite a distinct psychical phenomenon from desire: it is to be classed with volitions, thought it is, of course, specifically different from a volition initiating a particular immediate action.


  1. Maybe in fields that relate to psychology we should abandon the use of the word "always". Always is for hard scientists. Psychologists get to say "tends to" or "in most cases".

  2. Since when are definitions pointless? If BDI tells us nothing more than what we mean by "strength" when speaking of desires, isn't it still useful to know that that's what we mean so that we won't confuse it with other things (like the intensity of subjective feeling you allude to, for example)?

  3. Well, I think the common-sense notion of desire strength is more a matter of felt intensity than behavioural impact, so BDI is just poor conceptual analysis if it is meant to reveal "what we mean" in our ordinary use of these terms. Perhaps it is meant instead to stipulatively introduce a new technical term. But it does not seem to be a term that can do any useful theoretical work, for the reason I pointed out: BDI implies that we cannot tell what desires someone has until we see which act they perform. 'Desires' here are not states with any independent existence. They do no play any deep explanatory role. They're merely attributions that we make after the fact. (What's the phrase... a 'dormitus virtus' explanation? You know, that faculty that "explains" why we fall sleep.)

  4. Your argument here is like the argument that says that tries to defeat the theory of evolution by saying that it is circular. Evolution concerns itself with the survival of the fittest. However, the fittest is defined as those that survive. In this sense, the theory of evolution is trivial. If, instead, we try to adopt some independent standard of 'fittest', whatever standard we may try to adopt, renders the theory of evolution false.

    The answer is that 'survival of the fittest' is not, itself, a testable hypothesis. It is a principle from which testable hypothesi can be constructed.

    Again, it works like the principle that the acceleration on a body is equal to the vector sum of the forces acting on it. We can call this 'trivial' in virtue of the fact that if we ever found a body not accelerating according to the vector sums acting upon it, we would simply hypothesize another force. Indeed, that is what we do - and is exactly how scientists have come to postulate dark matter and dark energy.

  5. There's fortunately more to evolutionary theory than the empty claim that the fittest survive. But what more is there to BDI? How does it help us construct testable hypotheses (any better than the weaker claim that desires have motivational force)?

    (The physical law example is different. It is not 'trivial', but rather Moorean: better supported or less likely to be mistaken than any isolated measurement to the contrary.)


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