A lot of philosophers think that there are "merely justifying reasons", reasons that do not require action but can justify it. The defining feature of a merely justifying reason is that if one has a merely justifying reason to A, one can rationally refrain from Aing without needing any reason to do so. On the other hand, if one has a requiring reason to even a pro tanto one, to rationally refrain from Aing one needs a contrary reason.
I will argue against this based mainly on five plausible theses:
- One only acts rationally when one acts for reasons.
- When one has to do what one does not have rationally compelling reason to do, one is in bondage.
- One does not come to act in bondage simply because by not having reasons to act otherwise.
- Rationally compelling reasons are not merely justifying reasons.
- The status of a reason R as merely justifying does not depend on what other options are rationally available.
For my view of action, (1) is rock bottom. Claims (2) and (3) concern a concept of "bondage" that I don't have a very good characterization of. It is the opposite of the kind of freedom that Augustine and Leibniz talk about (Leibniz defines freedom as doing the best thing for the best reasons). Brainwashing produces bondage. There is bondage whenever a reason's action-causing force significantly exceeds its rational force. On the other hand, being compelled by one's virtue to do the right thing is not a case of bondage, even though a libertarian might worry that it's not a case of freedom (or only derivatively a case of freedom). Bondage is not necessarily opposed to responsibility. For our own freely chosen vicious activities can cause us to be in bondage. A compatibilist may think lack of bondage is necessary and sufficient for freedom. The libertarian is apt to think that it's necessary but not sufficient. Claim (4) seems very plausible. Now, maybe (5) can be disputed. One might think that whether a reason to A is merely justifying will depend on what reasons one has for other options. But that seems mistaken: the reason to A may become more or less opposed by the presence or absence of other options, but that shouldn't affect the status of the reason.
Now, imagine that I am the sort of being that can only act rationally (probably the notion I have in mind is something like minimal rationality). This surely does not make me be in bondage. Suppose that I rationally and freely choose to A for a reason R over some option B for which I have some other reason S. And consider a similar world W where I do not in fact have any reason to choose otherwise than to A. In that world, S doesn't support my choosing B. For instance, maybe in this world I choose to watch a movie for fun (and "for fun" seems to be a paradigm case of a merely justifying reason, if there are merely justifying reasons) over going to bed early to rest up more. But in W, going to bed early is known by me not to be restful. By (3), I don't come to be in bondage just by losing reasons, so in W my choice to A is still a choice not made in bondage. But in W, I have only one choice available supported by reasons, namely to A, and hence only one rational choice by (1). So if I can only act rationally, I have only one possibility available: to A. Since I am not in bondage, by (2) it follows that my reason R to A is rationally compelling. But a rationally compelling reason is not merely justifying, by (4). So, my reason R to A is not merely justifying in W. Hence, it is not merely justifying in the actual world. Thus, one does not rationally choose to A on the basis of a merely justifying reason.