"Reason is, and ought only to be the slave of the passions, and
can never pretend to any other office than to serve and obey them."
It seems true enough to say that many ethical issues could be better served and settled if only people handled them more reasonably. Too often ignorance, carelessness, and thoughtlessness infect moral choices, and if anything were to be the prime combatant of such negative influences, it would be reason.
But granted this, there is still an issue of primacy; namely, is reason --and should reason be-- the ultimate judge of moral actions? Many would surely say that it ought to be, but too frequently is not. Perhaps they would say that emotion and desire overtake the moral agent in far too many cases where calm reason would have been more appropriate.
I, however, disagree. Not only do I think that reason is not the ultimate judge of moral decisions, but I believe that it shouldn't be either. Reason plays an important role in ethics, to be certain, but that role is subservient to a more powerful faculty: passion. Interpreting some of Hume's ethical theory to support this claim, I would like to show that passion is the ultimate judge in our moral lives, and that reason is not as influential as some rationally prone thinkers might believe. This discussion, in turn, will raise some metaethical questions that I will pose later.
Passion, on the other hand, is not so functional. Passion (as a mass noun for passions in general) is more spontaneous and fundamental. Passions include basic emotions and desires, thus ranging from anger and lust to the craving for something sweet. They are not nearly as precise as the elements of reason, nor as clearly caused; what I mean is that a rational judgement can be traced from its conclusions to its various premises and logical connections, whereas a passion is often just there. Passions are not entirely mysterious or random, either, because certainly they can be excited by reasons in some cases. Nonetheless, I want to show, as David Hume did, that passion ultimately decides moral cases and properly so.
Before anyone condemns passion's potential for frivolity and freneticism, there is an immediate way to show its fundamental power over reason. Though it seems clear that reason shows us how to recognize phenomena and assess them, it leaves absent any reasons why... and by "reasons," I should more properly say "causes." Reason is a powerful tool that by itself lacks any initial motivation as well as any reactions to its conclusions. For example, in order to make money, reason will serve you well in recognizing the sources of money, how to access them, which will provide the most, and so on. But it is missing any motivation to make money and any point to the money once it's made.
Passion, however, is precisely the source of motivation. It is when one desires money, for example, that the rational process of making it gains any propulsion. Desires and emotions come first, and with these in mind, reason serves as a tool to most effectively fulfill those desires or satiate those emotions. And when I said there was no "point" to the conclusions of reason, I meant that there was no inherent meaning to them by themselves. As David Hume eloquently states in A Treatise of Human Nature, "'tis not contrary to reason to prefer the destruction of the whole world to the scratching of my finger." Why? Because reason alone has no preferences whatsoever. One's desires and emotions grant the fundamental preferences to moral decisions with which reason can then process accordingly (for example, one may have a great desire to stay alive, and reason can in turn use this strong desire as a premise in any rational analysis). Meaning is attained by rationality in so far as it fulfills one's desires and pleases one's emotions. To use the money example again, is it passion that reacts to the rational plan for making money by motivating action, or by ignoring it altogether. Passion is the part of us that is either fulfilled once money has been made, or remains dissatisfied, as the case may be.
Analogously, then, reason is like a calculator; powerful and precise (at least potentially when the analogy is applied to human rationality). But a calculator can't turn itself on, nor choose which numbers to process without some fundamental, initial commands first, nor take its various sums and subtractions and apply them to anything as to create meaning. It is a desire to calculate numbers that turns the calculator on; a desire for certain processes over others that tells the calculator what commands it ought to obey; and a desire to apply the results to some matter, that matter being rooted, fundamentally, in a desire or emotion which the calculation helps fulfill.
Furthermore, when a passion and a sole rational judgement collide, passion will always win out. A reasonable conclusion can only be preferred if it accompanies a desire that is stronger than the other passion. For example, one may be starving, but is offered a poisonous apple to eat. Despite that desire for food, reason tells this person that they will die if they eat it. This rational conclusion is motivated by the desire to live, and since that desire overrides the desire to eat, the person knows better than to eat something deadly.
Overall, I would not go so far as to say that reason is the "slave" of the passions, as Hume says. I would prefer to think of passion as a king and reason as his chief counselor. The king gives every initial command and assesses every result, but it's the advisor who informs the king and processes the details of executing his orders. Despite the regency of passion, the role of rationality is essential for the success of the kingdom. After all, the details it handles are significant factors in satisfying passion. Therefore, reason is still a necessary condition for making good moral judgements in that it provides the most effective ways to fulfill the greatest amount of desires, as well as prioritizing stronger desires over weaker ones. Nevertheless, passion frames and grounds everything reason does as such to make it the ultimate judge of moral cases.
This raises significant ethical questions. I would think that many people would find this biological grounding of morals in biology disheartening, maybe even dehumanizing. This, however, will not stand in the way of scientific research into the area, as such social sciences as evolutionary psychology are already progressing. To ground the reason why in the discussion above (and my own belief in pragmatism), research will override any possible discouragement simply because our desire for information that will help us better understand ourselves is greater overall than the desire to hold on to romantic perceptions of ourselves. After all, the conclusions such research will provide still gain their meaning and significance in so far as they fulfill our desires; therefore, maybe it's our desires that need reprioritizing if we are ever tempted to stay blissfully ignorant in such matters.
Furthermore, the tie that binds ethics to biology raises specific social and philosophical concerns. Can moral proclivity be chemically altered, even genetically programmed? Ought it to be? Again we face an issue of effectiveness versus potentially questionable means. Surely a drug that would help people cease from committing crimes would be of interest, but then a slew of issues unfolds concerning free will and human rights. This issue, I feel, is already upon us when medical doctors prescribe drugs to alleviate depression as they do now. Those who recommend more biologically rooted solutions need to consider the psychological effects of such means, and those who resist biological findings need to consider why exactly they are so resistant.
Personally, I would rather have my understanding of morality established in empirical research if that proved enlightening, even if its findings may seem initially disheartening. There is always a pragmatic way to assess this data afterwards which takes all factors into consideration, after all, including not only the desire for precision and empirical understanding, but psychological and personal desires as well.
To conclude this discussion, I still marvel at the coveted role so many thinkers perceive reason and rationality having. Few would argue that reason is not valuable --even necessary-- in our moral lives. Nonetheless, it is not the ultimate goal nor could it be. Even if one's strongest desire was to be rational, there would still be a need for other desires to motivate where this rationality ought to be applied. Ultimately, it is our passion that governs our moral decisions by motivating them, giving them meaning, and overseeing rationality's processes along the way. This seems fairly clear whether we like it or not... unless, I suppose, you desire to value rationality over passion more than you desire to hear good reasons otherwise. In that case, this discussion and any of its related ideas would move you not at all... and simply because you wanted it so.