Like many who saw him perform, I won't soon forget the Oscar-winning actor. Not because I witnessed him live on Broadway. Nor because I show one of his movies to students at the university where I teach. It's because he was undeniably human, both onscreen and now most certainly off.

Philadelphia native and screenwriter David Katz found Mr. Hoffman's body last Sunday morning in his West Village apartment in New York City, a syringe in his arm. He was, it turns out, a struggling addict who reportedly had not used for 23 years when he relapsed last year.

Insight, honesty, sensitivity

His finest performance was the one I witnessed in New York in 2003, which most people missed: "Long Day's Journey into Night," by Nobel-winning author, Eugene O'Neill. That afternoon, it should have been called "Hoffman's Long Day's Journey into Night."

That's because despite its all-star cast (Brian Dennehy and Vanessa Redgrave), it was Mr. Hoffman, portraying Jamie Tyrone — the bitterly ironic, alcoholic older brother to the sickly poet son — who reached into the wings of the Plymouth Theater and didn't let me go for more than three straight hours.

Every line, every gesture was that of a young man revealing his demons authentically — the deprecating humor, the guilt, the shame. Mr. Hoffman seemed to me the only one that night making something entirely new — not from the lines of a fusty play that takes place on a single evening in 1912, but from his own insight and sensitivity unattainable by other thespians.

I knew nothing of Mr. Hoffman's demons at the time. (And I still don't.) One thing was for certain: He had them. That's because actors who are great, but who aren't real alcoholics, fail to convincingly play them on stage or screen. Not Mr. Hoffman: He told a New York Times Magazine reporter that the performance "nearly killed" him.

I knew it because I had been sober myself for about 11 years by the time I saw the play. I knew it also because, by the end of the show, when the sharp light of a late-summer New York afternoon struck me in the eye, I wanted one of two things: to have a stiff scotch myself or to bawl my eyes out. I thankfully did the latter.

My reaction was for the real character Mr. Hoffman played: I had read the biography of O'Neill the playwright, whose own tormented older brother drank himself to death at age 45. (Mr. Hoffman was just a year older when he died Sunday.)

Reasons to cry, reasons to live

My tears were also for the actor himself. What Mr. Hoffman grappled with was so honest and true and exhaustingly painful that there seemed no right response other than to applaud for 10 straight minutes, my eyes watery. I turned to my wife and said, "How can he sleep at night?" It would sap the life out of an actor twice as experienced.

I wonder today whether the grief was for my own demons just around the corner. They came barreling into my own life within a month of witnessing Mr. Hoffman on stage. When my baby sister — an artist, age 35, mother of two young children — died in an automobile accident near Bodega Bay, California. When I heard that news, I wanted a drink more than I ever had before. Instead, I bawled, and made the decision to hold onto my own sobriety like the drowning cling to a raft.

I lived. Mr. Hoffman died. So it goes with addicts and alcoholics.

His passing has nonetheless unleashed complex issues: the epidemic return of heroin to Philadelphia and most every other large American city. The increasing crossover of consumers from painkillers to the less-costly hits of heroin. Not just in young people so much as a new group: suburban 45- to 54-year-olds. And even more dangerous than heroin alone: the addition of painkillers 100-times more powerful than morphine.

Then there's the question of the responsibility of the dealer for the user's death (four of Mr. Hoffman's alleged dealers have been arrested), and last but not least, the death of the so-called "greats" (musicians, actors, writers) by accidental overdose (Charlie Parker, Elvis, Heath Ledger).

How good he was

Beyond the unsolvable issues raised by his death, what remains for me is the work. Mr. Hoffman leaves behind not just three children and a long-time partner, but more than 60 films and plays. He never went for showy, leading-man, megastar roles like his contemporaries. He didn't play characters whom audiences idolized. He played opposites, characters no one wanted to be, or to have come near children.

From loser-loners to men both strong and shattered, he did self-loathing, rage, and coolness at the drop of a dime. Intense, intelligent, relentless in his pursuit of becoming the character he portrayed, he seemed wholly new, beyond the previous generation's method actors.

Every semester at the university where I teach, I show one of his films.

My students first read "In Cold Blood," the 1966 book that altered American letters and made, and then unmade, its writer, Truman Capote. Unlike Mr. Hoffman, Capote spiraled for years into a shamelessly, self-embarrassing shell of his former self and died an alcoholic and prescription pill addict in 1984.

Then I show the class the film "Capote." My students consistently express surprise at hearing Capote's voice as portrayed by Mr. Hoffman. He didn't really talk that way, they tell me. Yet by the end, they too are won over by Mr. Hoffman's Oscar-winning performance.

In the movie, he says something like, "When I think of how good my book is going to be, I can't breathe."

Now that Philip Seymour Hoffman has left us so suddenly and pointlessly, when I think of how good he actually was, I can't breathe either.

Michael Carolan teaches writing and literature at Clark University. He lives in Western Massachusetts with his wife and two children.