Thomas found himself laughing with her, struck by how quickly she had managed to turn his mood. There was something about her smile, a kind of open-mouthed honesty, that spoke of loving, irreverent parents and a childhood spent joking around the dinner table. He couldn't help but wonder how much they had in common. 'The boss thought I was your kind of people.'

'Which is why,' Agent Logan said, ducking her head as she lingered on the word—an oddly endearing gesture, 'we could use your help on this case.'

He snorted skeptically. 'What you guys need is a neurologist.'

'A psychologist isn't close enough?'

Thomas shrugged. 'Neurology is the science of the brain. Psychology is the science of the mind. Simple enough, I suppose, but things get very complicated very fast when it comes to understanding the relationship between the two.'

'The relationship of the mind to the brain?'

Thomas nodded into his beer. 'Some say the mind and the brain are actually the same thing, but at different levels of description. Others say they're entirely different things. And still others say only the brain is real—that the mind, and therefore psychology, is bunk.'

'What do you say?'

'I honestly don't know. The scary thing for me is that as the years pass and neuroscience matures, the relationship between the two disciplines starts to seem more and more like that between astronomy and astrology, or chemistry and alchemy.'

'And why's that?'

He paused, struck by the selfless candor of her expression. In his never-ending effort to engage his students, he had memorized innumerable little 'factoids' regarding this or that freshman preoccupation. As a result, he knew far too much about the myths and details of attraction. He knew, for instance, that Sam possessed all the features that men in Western cultures found appealing: large eyes, slender nose, high cheeks and delicate jaw. He knew that, no matter what the circumstances, simply looking at her would light up the reward centers of most men's brains.

His own included.

'Because neurology is a natural science,' he replied after a glutinous cough. 'It looks at human behavior and consciousness as natural processes like any other process in the natural world. It actually provides causal explanations for what we are.'

'And psychology doesn't?'

'Not really, no. Psychology also involves something called "intentional explanations", which are pretty tricky from a scientific point of view.' He found himself breathing deeply, as though steeling himself for some arduous task. 'For instance, why did you take a sip of your beer just now?'

Samantha frowned, shrugged. 'Because I wanted to,' she said lamely.

'There you go. That's an intentional explanation. A psychological explanation. This is largely how human beings explain and understand themselves: in terms of intentions, desires, purposes, hopes, and so on. We use intentional explanations.'

'And they're not scientific?'