One day earlier this month, Sean Dorrance Kelly was at work in his sunny Emerson Hall office. On one side of his desk were books — a ceiling-high, room-wide stack of tomes ranging from Greek editions of Homer and contemporary works of neuroscience to books on twenthieth-century French, German, and Anglo-American philosophy.

On the other side, scrawled on a whiteboard, was a stick-figure man looking at a little car. Lines bounced off the car back into the man’s eyes and into his brain.

Those lines suggest the basic questions that attracted Kelly to philosophy in the first place. “I’m interested in perception,” he said. “What it is to see stuff. What our relationship is to things when we have an experience of them.”

Behind those basic questions is a bigger one, which in some sense defines the centuries-old pursuit of philosophy, from Heraclitus and the Buddha to the present. “I want to know what it is to be a human being,” said Kelly, 39, who arrived at Harvard last year after a seven-year stint at Princeton. “What it’s like to be what we are.”

To get at this big question, the Ohio native explores visual experience, examining as a psychologist would what a person normally sees. But Kelly also pursues phenomenological questions, looking at what it’s like to have experiences.

And he looks at the literary or artistic characterizations of experience — as in Proust, said Kelly, who was “trying to get at the richness and the depth” of his memories.

As an undergraduate at Brown University, Kelly thought the best way to explore the big questions of life was through mathematics and its manifest proofs. His bachelor’s degree is in mathematics and computer science (1989).

At the same time, he studied neuroscience and artificial intelligence as a way to begin to answer the big questions. So Kelly — who still dabbles in amateur robotics — turned to the study of neural network models of brain activity. While still in his fourth year of college, he proved several theorems about the computational properties of neural nets; on the basis of this work, Brown awarded him a master’s degree in cognitive and linguistic sciences.

At the University of California, Berkeley, he started Ph.D. work in logic and the methodology of science.

“But it was unsatisfying — I didn’t feel I was learning what I wanted to learn,” said Kelly. “Eventually, I found my way to philosophy,” taking a Berkeley Ph.D. in 1998 — and teaching the humanities at Stanford for a year after that.

At Princeton, Kelly taught philosophy and neuroscience, and was an affiliated investigator at Princeton’s Center for the Study of Brain, Mind, and Behavior.

At Harvard, Kelly’s research and teaching retains a flavor of the broad academic searches that mark his career. He taught Humanities 14 last fall, a course on existentialism in literature and film. This spring, it was Philosophy 156 — philosophy of mind — in which students looked at mind-body connections, consciousness, and the nature of intentionality.

Kelly’s wide academic range has made another mark: He’s the first philosopher since the celebrated William James (1842-1910) to have a laboratory at Harvard. For James, trained as a medical doctor, it was a space in Lawrence Hall, destroyed by fire in 1970.

For Kelly, it’s 300 square feet in Vanserg Hall, where he and a team of graduate students conduct psychophysics experiments — to answer “very tiny questions” that lend themselves to empirical experiments, he said.

Here’s one: If you look at a penny at an angle, it normally looks circular; but you can also see it, as painters may, as elliptical. But can you have both of these experiences at once?

Kelly thought not, but he wanted to test it out. He used what is known in the psychophysical literature as the “shape-priming effect,” in which a person is primed to prefer one shape over the other by seeing it ahead of time. It has turned out, as Kelly predicted, that subjects primed by seeing the tilted penny could more quickly spot circles than ellipses.

The lab will stay in operation while Kelly is on sabbatical next year, working on three planned books in his new Arlington, Mass., home and making periodic visits to campus. He has also enjoyed working with undergraduates at Harvard so much, Kelly said, that he plans to keep his small undergraduate reading group active during his sabbatical year. They’re slowly making their way through Jean-Paul Sartre’s “Being and Nothingness.”

Kelly’s research often explores the dense and difficult French and German philosophers of the last century: the phenomenology of Edmund Husserl, which investigates meaning and consciousness, and the existential philosophy of Heidegger, Sartre, and Merleau-Ponty, with their focus on meaning and engagement.

He’s trying to sum up his understanding of these groundbreaking philosophers in a coming book, “Wonder in the Face of the World: Classical Phenomenology for Philosophers of Mind.”

All of these thinkers represent points along a continuum of thought that, since the seventeenth century, has contributed to the disappearance of God by moving human beings to the center of reality, said Kelly.

In the eighteenth century, Kant interpreted humans as “self-law givers” — autonomous beings who are themselves the only source of universal moral constraints. Nietzsche went further, positing the “free spirit’’ — the being who gives himself his own individual constraints — as the highest form of human existence.

But a world without God and without external constraints is a lonely and disenchanted world. That raises a timely modern question, said Kelly: Can we regain a notion of the sacred, even in our secular world?

He’s reaching back in time for an answer — by writing a book (with Berkeley’s Hubert Dreyfus ‘51) on the notion of the sacred in Homer. In those times, gods provided humans with a sense of external authority that was nevertheless not a universal law.

By drawing on the example of Homeric Greece, the modern age may be able to recapture “the beginnings of a notion of the sacred in modern life,” said Kelly. “In this way, one can hope to re-enchant the world.”

Philosophy can do the same job that good painting or sculpture or poetry do, he said — “to do justice to experience writ large.”

That brings up another big question Kelly is exploring: What is the “right account” of perceptual experience? he asked, “one that lays out in detail all the subtle and nuanced aspects of our experiences” — as Proust, or Melville, or Cezanne, or Homer might in their own ways.

Kelly is writing a related book, tentatively titled “Seeing Things.” It will be an exploration of “all the complicated and subtle and amazing things that go on when we perceive an object,” he said.

Back in his office, underneath the drawing of the stick figure looking at the car, is a drawing of a baseball player at bat. That might sum up Kelly’s life at home with wife, Cheryl Kelly Chen, a lecturer in Philosophy at Harvard, and their son, Benjamin, who will turn 3 in June.

“We’re hoping Ben will be the opposite of a philosopher,” said Kelly, a recreational runner and swimmer who was a standout backstroker at Brown. “I’m thinking, maybe, a shortstop.”