This week we explored the ultimate nature of human motivation (see my videos here, here, and here). Let’s say Reyna risks her livelihood to convince her friend Kylo Ron to leave his evil organization and join her good one. Why would she do so? A psychological egoist would say Reyna must do so because she is getting something out of it, even if she doesn’t realize this. It may be that Kylo Ron would be a great asset to her organization or maybe she will just feel good about herself for helping him. Whatever it is, it is ultimately because of the benefit to her that she actually chooses to do so, even if it appears to her that it is for another reason. A psychological altruist believes Reyna might help Kylo Ron s olely for his sake, even if she gets some benefit as well. A final view believes Reyna might help Kylo Ron just because she feels a sense of duty or obligation to help out those in need.
One thing that is interesting about this question is that it is an empirical one, so it’s not solely–or even essentially–the domain of philosophy. It is tempting to project our philosophy onto the situation. We might, for example, want Reyna to act altruistically because we believe acting selflessly is what makes an act moral. Or we might want it to be impossible that Reyna act any way but selfishly because we believe capitalism requires acting in our own best interests. However, if we are asking why someone made a particular choice, there is no pre-theoretical reason to believe one way or the other. Instead, we must look to science for an explanation.
It is the job of the experimental psychologist to determine the actual motivation of a human choice. She must devise experiments in which human agents are presented with a choice and the most reasonable prediction differs given each possible view. Subjects should then be tested accordingly with all appropriate variables controlled (e.g., subjects should probably not know they are being observed at the time). The result will tell us what actually motivates human choice. For example, if the hypothesis is that Reyna is
only helping Kylo Ron because he will help her organization, have Kylo Ron pretend to lose his powers. If it’s that Reyna just wants to feel good about herself for helping, devise a way that she would feel bad for helping (e.g., maybe everybody, including Kylo, would tell her they would hate her for helping him). After whittling away possible motivations, we will hopefully be left with the true one.
We may be tempted to think that if this is the case, why do we even need philosophy? Here are three ways philosophy is important in this question.
First, we use philosophy to clarify the question. I said we are asking what does motivate human choice, but we could also be asking what could and what should motivate our choices. The latter question can be pragmatic or ethical, but it is not a scientific question. However, as we saw on the video, it is easy to confuse these questions. A philosopher can help untangle issues like this.
Second, philosophy can help us clarify our terms. For example, a psychological egoist might claim Reyna is acting selfishly because she is fulfilling her desires. This can’t be right, however, because Reyna might 
desire what is best for Kylo Ron. If that’s the case, then she would be acting altruistically. So, if a scientist were to devise a test to see if Reyna acts without any desires, she would be missing the whole point. Analyzing concepts is a philosopher’s job, not a psychologist’s, so philosophy is an important tool here.
Finally, experimental psychology is not as precise as some sciences, such as physics. Sometimes science gives us great evidence for believing a theory, but that is usually when we can easily measure things. The reasons and desires of people are opaque to observers because they reside in the mind, and we cannot see the minds of others. We can observe our own minds, but only reflectively. It may be the case the experimental psychology gives us some reasons to think one way, but philosophy is needed to push us over the edge into belief. For example, maybe Reyna chooses to help Kylo Ron even to her own detriment, but there is always the possibility that she is self-deceived and subconsciously believes everything will work out alright. However, if philosophy could (and I’m not saying it can) give us a solid account of free will, we could show how Reyna’s altruistic choice is at least possible, and this would give us reason to believe that she really did want what’s best for Kylo Ron. Even if he did kill Don Solo.