Every ought simply has no sense and meaning except in relation to threatened punishment or promised reward … Thus every ought is necessarily conditioned through punishment or reward, hence, to put it in Kant’s terms, essentially and inevitably hypothetical and never, as he maintains categorical … Therefore an absolute ought is simply a contradictio in adjecto.” —Schopenhauer (On the Basis of Morals, §4).
Imperatives (oughts) are directives; they command us to perform or abstain from certain behaviors. The philosopher Immanuel Kant split imperatives into 2 types; Hypothetical and categorical. Hypothetical imperatives (aka rational oughts) instruct what actions to perform in order to achieve a particular goal. Example: “If you want to lose weight you ought to diet and exercise.”
Hypothetical imperatives are only applicable to persons who want to achieve a particular goal.
If you don’t care about losing weight the “you ought to diet and exercise” isn’t applicable to you as there would be no motivating reason to diet and exercise.
According to Kant, moral oughts (categorical imperatives) are not of this sort. Categorical imperatives have nothing to do with achieving goals, losing weight, or avoiding pain etc.
For Kant Moral behaviors aren’t about staying out of prison, or avoiding certain social consequences. Unlike hypothetical imperatives, categorical imperatives (purportedly) instruct us how to behave irrespective of our desires, whims, preferences, and goals.
Morality doesn’t state “If you want to achieve X you ought to do Y.”
Rather, it says “Thou shalt not commit murder!” regardless of whether you are concerned about facing the death penalty or not! It is this kind of imperative the moral skeptic rejects, because outside of the context of punishment and reward there can be no motivating force to propel one to act in a certain manner.
After all, if I want to do X and can get away with performing X without consequence why ought I not do so? Because it’s ‘wrong’? What does ‘wrong’ even mean? Hence the nihilist contends that only hypothetical imperatives are tenable. The categorical imperative is nothing but the ethical woo of moralizing sophists!
A prescription by itself (a non hypothetical imperative) is neither true or false as it lacks true or false conditions. Consider the prescription “Thou shalt not steal”. If there is no assumed if clause (goal) it is merely a command. It is expressing a desire for persons not to engage in a particular activity.
It isn’t a proposition. In philosophy a proposition is the content of a sentence which asserts or denies a certain state of affairs. “John is not a female” for example is a proposition because it is asserting something about empirical reality.
It is either describing reality accurately or it isn’t. But under what conditions can an isolated “ought” or “ought not” be rendered true or false?
Now, I would like to point out that while it is true that in everyday speech the if clause (the goal) is often omitted—it is still implied.
For example a father may tell his son “You ought to brush your teeth”. In such an instance the if clause (goal) is implied and is something akin to “so that you can keep your teeth healthy”.
It may be uttered in a forceful authoritative tone and thus acting both as a command and a description of what must be done in order to maintain dental health.
In this case the “ought” is used both as an expression of desire and a description of what must be done to attain a certain end.
Moral prescriptions are not like this. They do not depict reality, they are expressions of desire, and attempts to motivate and influence others.
With that said, there are those who may believe that their prescriptions refer to some kind of normative fact about the world. In such cases I believe the “ought” is indicative of mistaken belief rather than a mere expression of attitude.