One potential objection to Desire Utilitarianism came from the 18th-century Scottish philosopher David Hume.
In A Treatise of Human Nature, Hume added, almost as an afterthought, an objection that he said would defeat all 'vulgar systems of morality':
"In every system of morality, which I have hitherto met with, I have always remark'd, that the author proceeds for some time in the ordinary ways of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when all of a sudden I am surpriz'd to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, 'tis necessary that it shou'd be observ'd and explain'd; and at the same time that a reason should be given; for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it."
Desire utilitarianism holds that it is quite possible to construct an argument consisting entirely of 'is' premises, yet yielding an 'ought' conclusion. That argument would have the following form:
Premise 1: A set 'is' statements describing reasons for action that exist.
Premise 2: A set of 'is' statements that describe the relationship between possible actions and the reasons for action that exist.
Conclusion: An 'ought' conclusion of the form that the agent 'ought' to do that action for which the most and strongest reasons for action exist.
Hume's objection is that the 'ought' term in the conclusion is a different type of relationship from the 'is' claims in the premises. Therefore, the conclusion cannot follow from the premises.
Desire utilitarianism answers this by saying that 'ought' is not a different sort of relation. 'Ought' can be reduced to 'is recommended by the most and strongest of the relevant reasons for action,' where the relevant reasons for action are those listed in the premises. As an 'is' statement, an 'ought' conclusion can well be derived from other 'is' statements, as long as those 'is' premises included one or more true premises about reasons for action.
Furthermore, desire utilitarianism holds that desires are the only reasons for action that exists, so a true premise that mentions reasons for action must be a premise that mentions one or more desires.
Hume himself writes in favor of this type of interpretation.
When discussing virtue, Hume identifies four characteristics that are relevant to the measure of any given mental quality. Every one of these can be expressed in terms of an 'is' proposition.
(1) Is agreeable to self
(2) Is useful to self
(3) Is agreeable to others
(4) Is useful to others.
Desire utilitarianism identifies these same four qualities, expressing them in terms of desires. A virtue is a desire (mental quality) that is such as to fulfill, directly (agreeable) and/or indirectly (useful) the desires of self and/or others.
Furthermore, Hume identifies these foundations for virtue as facts.
Nothing can be more real, or concern us more, than our own sentiments of pleasure and uneasiness; and if these be favourable to virtue, and unfavourable to vice, no more can be requisite to the regulation of our conduct and behaviour.
Here, Hume is speaking only of 'Is agreeable to self', as if this is the sole criteria for morality. This is the view of common subjectivism, which is inconsistent with desire utilitarianism. Yet, whether we accept 'is agreeable to self' or 'is agreeable and/or useful to self and/or others' as our measure of virtue, we derive value from an 'is' statement - from a fact.
Another argument against the thesis that there is an is-ought distinction is that, if true, it requires some sort of metaphysical dualism.
According to this line of reasoning, there is no distinction between 'is' and 'ought'. There is only a distinction between 'is' and 'is not'. 'Ought' either has to fit into the category of 'is', or it must fit into the category of 'is not'. Putting 'ought' in a third category - a category of 'is' yet somehow capable of interacting with what 'is', requires an extraordinary metaphysics which opens up a whole host of questions. What is this mysterious 'ought'? How are we aware of its existence? How does it intereact with the world of 'is'? How can there even be a property of 'ought'? The theory is so remarkable that, unless somebody can actually work out the details in a satisfactory manner, we are best off assuming that 'ought' exists in the realm of 'is', or it does not exist at all.