Love, passion, and obsession are three temperatures of one fever, and most of us have mistaken one for another at the worst possible moment.

Love is room temperature. It is warm without effort, and nobody notices it until it leaves. It looks like a husband who knows how his wife takes her tea and cannot say when he learned. Love wants the other person to flourish, even in directions that bypass the kitchen.

Passion is a stove. It heats the room, cooks the dinner, and burns the hand that grabs the pot. Passion wants the other person, and it wants them tonight. It supplies the nerve for sentences like “Let’s quit our jobs and open a bakery.” It is the reason poems exist and the reason divorce lawyers own boats. Passion is honest about one thing: it cannot sustain that heat, and it does not pretend to.

Obsession is a stove with the dial snapped off. It wants neither the person nor the person’s flourishing. It wants the wanting. Gatsby does not love Daisy; he loves the green light at the end of her dock, a lamp he lit himself. Reaching is the point, and arriving would end the feeling. That is why obsession survives rejection, silence, and, in Gatsby’s case, the object’s marriage to someone else. It requires no cooperation from the person it claims to adore. It often works better without.

The test is simple. Imagine the person happy, far away, and not thinking of you. Love is glad. Passion sulks for a week and recovers. Obsession takes it as an insult and starts drafting a reply.

The borders between the three are porous. Every large undertaking of the mind, a novel or a theorem or a decade of mastering one instrument, is an obsession in a good suit. We call it dedication when it produces something and a problem when it produces only the dedicated. The difference lies in the object. Obsession with a person consumes the person. Obsession with work consumes only the weekends, and the work, unlike the person, does not file for separation.

So passion is how love begins, and obsession is how love spoils. The dial that separates them is your tolerance for the other person’s independence. Love is the only one of the three that can watch you leave and keep the lamp lit.