As I’ve argued recently, useful fictions have their place in a respectable epistemic toolkit. Some theoretical apparatuses must simplify or caricaturize their target phenomena in order to allow us to get a grasp on things (for example, talking and thinking like naïve color realists allows us to track different objects’ dispositions to evoke particular colorful experiences, though they do not possess the “objective colors” we impute to them).
However, I do not wish to give the impression of being soft on falsehood. Not all fictions are equal, and most will mislead us, even if they have some degree of instrumental utility. Read that again: Even the pragmatist who equates truth with usefulness needs a way to distinguish prudence from mere and lazy expedience.
The expedient belief passes a first-glance test of likelihood, and might even teach us a new trick for manipulating our environment. But even if it appears to explain existing facts, it will fail to gain substantiation in ongoing observation; afford few or no new predictions; or grant us only a slippery hold on the phenomena we attempt to influence.
For example, a student might more effectively study for her finals if she believes that willpower is an unlimited resource. However, the fact that accepting this theory helps her with one task (studying) cannot by itself decisively validate the theory. The pragmatic maxim, as always, is helpful to clarify this point. When considering the truthfulness of a claim, Peirce urged inquirers to consider all the effects that would obtain if a given hypothesis were true. The key here is that all effects must be considered, not only those relevant to a particular task or experiment. In this case, the reality of self-control’s finiteness has effects that cannot help but exert themselves. Our student might eventually realize that even during a good stretch of studying she has to take breaks to replenish herself; that even people of exemplary willpower who consistently push themselves always eventually burn out; that no matter how many Red Bulls she pounds, she can’t pull an all-nighter every night, etc.
Therefore, for our student to assent to the limitlessness of willpower contradicts experience, and moreover, limits her ability to successfully pursue her own goals (e.g. if she works on a group project under the assumption that her teammates are limitless wells of self-control, she’s less likely to end up with an exemplary final project than she is shoddy work made by worn-out, disgruntled colleagues). In the long run, our student will be hampered, not helped, by her belief in indefatigability. The limitlessness of willpower will reveal itself as a useless fiction.