On Desire 2018. Part 44: Appetites as Beliefs About Reasons

In considering objections to his thesis, Gregory considers an objection near to the objections I have raised. Specifically, he considers the objection that it makes no sense to think of appetites (such as hunger) as beliefs about reasons to eat.

Recall, Gregory’s thesis is:

To desire to φ is to believe that you have normative reason to φ.

(Gregory, Alex, (2017), “Might Desires Be Beliefs about Normative Reasons for Action?” In Deonna J. & Lauria F. (eds). The Nature of Desire. Oxford University Press.)

So, on Gregory’s account, to desire to eat is to believe that one has reason to eat. It is absurd to think that a desire to eat is a belief that one has reason to eat. Therefore, we should reject a Gregory’s account.

Gregory attempts to defend his thesis be distinguishing the feeling of hunger from the desire to eat. We can have the desire without the feeling, he argues, as when one eats to be polite. And we can have the desire without feeling hungry, as when we have desert. The feelings of hunger are not beliefs about reasons to eat or anything else. However, the feelings are not the desire to eat, so this leaves open the possibility that the desire to eat is a belief about reasons.

I wonder if Gregory ever wanted to lose weight. That experience alone demonstrates that the desire to eat is independent of any and all beliefs about having reasons to eat. There are a great many obese and overweight people who are fully aware that they have no reason to - and many reasons not to - eat, but are driven to eat by an overwhelming desire. There are also a lot of people of normal weight who constantly struggle against a desire to eat that does not go away just because one rehearses the reasons.

We know something about hunger. For one thing, eating behavior is associated with the hormone ghrelin. Ghrelin is released by the stomach when it is empty, and stops being released when the stomach is full. Empirical research shows that the concentration of this hormone determines eating behavior. Note that the experiments that researchers have conducted on animals do not associate amounts of ghrelin with feelings of hunger. Researchers, so far as I can tell, have no way to determine what subjective sensations their non-human research subjects are feeling as a result of the concentration of ghrelin in their system. They only measure the disposition to eat, and their findings show that the disposition to eat is not only associated with ghrelin concentrations in the bloodstream, but with the amount of those concentrations. The more ghrelin, the stronger the disposition to eat.

On Gregory's model, the desire to eat is the belief that one has a normative reason to eat. The disposition to eat is influenced by the concentration of ghrelin in the system. Consequently, we seem to be required to imagine a system where the concentration of ghrelin somehow influences the belief that one has a normative reason to eat.

One of the ways that this can happen, of course, is that the concentration of ghrelin determines one's reason to eat which, in turn, determines one's beliefs about one's reasons to eat. However, if we get a reason to eat from the concentration of ghrelin itself, there doesn't seem to be anything else for the belief that one has a reason to eat to do. We can simply go with the reason to eat (the desire to eat) that the ghrelin produces.

Imagine if there was a drug where, with a small dose of the drug, you would believe that the surface of the sun has a temperature of 3000 degrees. However, with higher concentrations of the drug, you come to believe that the surface of the sun has a higher temperature. At double the concentration, you believe that the temperature of the surface of the sun is 6000 degrees.

There is another problem with this thesis, given Gregory's defense of his thesis. The concentration of ghrelin in the system is not subject to evidence. There is no logical proof that entails, as a matter of deductive reasoning, a different concentration of ghrelin and, with it, a different belief about the importance that eating has to the agent.

These, then, three problems with Gregory's account of appetites. First, there seem to be a lot of large gaps between what an agent believes he has reason to do (has reason to eat or to drink) and what he desires to eat and drink. Second, Gregory needs an account of the relationship between concentrations of ghrelin in the system and the belief about how much of a reason one has to eat - which is an odd type of relationship to have. Third, concentrations of ghrelin in the bloodstream is not subject to evidence.

An alternative option - the option that I would favor (the assignment theory of desire) - says that the desire to eat is the assignment of a value indicating the importance to the agent of the proposition "I am eating" being true. The amount of ghrelin in the system can simply be associated with the value assigned to the proposition being true. The more ghrelin, the higher the assigned value. The desire itself provides the reason to - and the motivation to - eat.

Appetites cannot, in fact, be easily reduced to what an agent believes he has a normative reason to do.