Suppose that a neuroscientist is studying love, and she discovers that romantic infatuation is caused by high serotonin levels, while attachment is caused by oxytocin. Has she actually learned anything about love? More generally, what is the significance of discovering neural or hormonal correlates to particular human emotions or behavior?

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Depends, of course, on what you mean by "love". Some philosophers and cognitive scientists distinguish between the (neuro)physiology of emotions like love and the phenomenal experience of love; others say that "they" are really the same, perhaps merely experienced from different points of view.

If your neuroscientist is studying the phenomenal experience, then she has learned of a neurological correlate of at least one or two aspects of that experience. It's unlikely that she's learned how that neurological correlate gives rise to, or causes, the phenomenal experience, though some philosophers and cognitive scientists (such as the Churchlands) believe that eventually we'll cease talking in such terms (just as we no longer speak of diseases being caused by evil spirits).

There is a famous (or infamous) thought experiment that is relevant to your question, but that reverses the roles a bit. You seem to have in mind someone who already knows about the phenomenal experience (in this case, of love) and is learning about its neurophysiological correlate. The thought experiment concerns a scientist (Mary) who knows all the neurophysiological facts about color perception but has never experienced colors other than black and white. When she first experiences red, has she learned anything new?

For more on this, see:

# Jackson, Frank (1982), "Epiphenomenal Qualia", Philosophical Quarterly 32: 127-136.
# Jackson, Frank (1986), "What Mary Didn't Know", Journal of Philosophy 83: 291-295.
# Ludlow, P., Y. Nagasawa, & D. Stoljar (eds.) (2004), There's Something About Mary (MIT Press).

as well as a wonderful literary treatment in:

Lodge, David (2001), Thinks... (Viking).

An interesting question. Of course, our neuroscientist has learnt something about love, for she has learnt something about the neural causes of certain feelings bound up with love. But you might well feel that there is a sense in which her discoveries don't help us understand what really matters about love as part of human life (hasn't in the important sense learnt about the nature of love). That needs a quite different sort of enquiry, pursued by poets and playwrights and novelists down the ages. Compare: someone who tells us about the chemical composition of the pigments used in Botticelli's Primavera has told us something about the painting. But again such discoveries don't help us understand the painting in the way that matters, as a work of art, as part of the human world: understanding that requires something quite different from chemistry.

We could stop there. But perhaps there is a bit more that needs to be said. For there can remain a nagging feeling that the neuroscientist has in some sense diminished love, shown that it is "just chemistry". Yet is that right? Must finding out about various causes and correlates of mental states in some sense undermine them, unmask them as not what we thought them to be? Well, let's consider various other cases before turning back to love.

Start with beliefs. What causes me to believe that there's a computer screen in front of me right now? No doubt there is a long and complicated physical story to be told -- light emitted by the screen, affecting my eyes, rods and cones in the retina doing their stuff, signals going up the optic nerve, etc. etc. All very interesting -- and of course not at all worrying! To be told that such a belief is produced by a lot of causal processes of that kind doesn't in any way undermine the belief. On the contrary: I postively want my perceptual beliefs about the world to be caused by the appropriate functioning of my sensory apparatus as reliable generators of true beliefs.

But other beliefs might be caused in less desirable ways. Jack's religious beliefs, say, may be causally grounded in stories prevalent in the community he was brought up in, and be causally sustained e.g. by the emotional comfort they bring him in bonding him to that community. And when he comes to realize that, then this fact might indeed be worrying: for he might well think, on reflection, that those kinds of causal processes aren't particularly liable to produce true beliefs (given that the same sort of processes functioning in other religious communities produce quite different beliefs). In this case, the causal explanation might well be regarded us "unmasking" the belief, revealing it to be not in good order.

What about desires? Why do I desire chocolate, say. One account has it that there are chemicals in chocolate that in a mild way act rather like THC (the active ingredient of cannabis). Interesting if true. No wonder I like chocolate! And coming to believe this account which explains my desire doesn't do anything to diminish my desire, or unmask it as inappropriate.

With other desires, however, it can be different. Coming to recognize the cause of a desire can diminish it. If it dawns on me that I want SuperDuperExpensive Corn Flakes rather than ValueOwnBrand Flakes, not because they are better, but only because I've been manipulated by clever advertising, then my preferences have been "unmasked" and may well change as a consequence.

So like the belief case, coming to discover the causes of desires can leave them in place in certain cases, but might be undermining in other cases.

And now what about romantic love? If Mercutio whispers in Romeo's ear, "It's the serotonin, old chap", will that change his feelings for Juliet? Has his love been rudely unmasked, e.g. as just a desire for cheap chemical thrills?

I don't suppose Romeo is much in the mood to be distracted by such thoughts. But, waiting for Juliet's household to get to bed so he can climb up to her balcony, he might reflect how interesting the chemistry of love must be (and one day, when he has less pressing business to attend to, he must learn more about it). He also recalls his school-room reading of Book One of Plato's Republic, and the old man Cephalus calming accepting that "the pleasures of youth and love are fled away". But Romeo is only too glad that he is young, his chemical systems are bursting with vim and vigour, and his brain still gets awash with serotonin at the sight of a pretty girl. He is very happy, so to speak, to go with the chemical flow. So Romeo's feelings for Juliet aren't changed in the slightest by reflecting on their neural causes any more than my belief that there is a screen in front of me and my desire for chocolate are changed by reflecting on their causes. And he'll think that the fact that his feelings have a "chemical composition" no more shows that they are just chemistry (in any important sense) than our scientist showed that Primavera is just a load of old chemicals! His feelings have a role and place in his life that he values, and it is that which matters about them.

I'm with Romeo on this.

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