In reality, we ratio­nalize. We deny, or we couldn’t go on living,” says Judah Rosen­thal, the suc­cessful oph­thal­mol­o­gist whose per­fect life begins to unravel in Woody Allen’s 1989 film, “Crimes and Mis­de­meanors.” In order to go on living, Rosen­thal must ratio­nalize the series of risky and unchar­ac­ter­istic deci­sions that nearly destroy him.

Dis­cussing the Allen film with a packed audi­ence at the Coolidge Corner Theatre’s Sci­ence on Screen event on Monday night, David DeSteno, asso­ciate pro­fessor of psy­chology in the Col­lege of Sci­ence, asked, “Why do any of us some­times act in ways that sur­prise ourselves…ways that, quite frankly, are out of character?”

The Sci­ence on Screen events pair film screen­ings  with intro­duc­tions by notable fig­ures from the world of sci­ence, tech­nology and med­i­cine. The films serve as an oppor­tu­nity for the speakers to dis­cuss cur­rent sci­en­tific research or tech­no­log­ical advances.

Crimes and Mis­de­meanors” served as a chance to explore research on char­acter. The stan­dard view of char­acter takes a black-​​and-​​white approach, in which the seven deadly sins will lead one to a life of misery and the seven heav­enly virtues will make for a happy, suc­cessful person.

But is pride always bad? Is chastity always good? DeSteno noted that pride can make us strive to gain resources, and chastity, if always adhered to, would mean the extinc­tion of our species.

The problem with this,” DeSteno said, “is that it log­i­cally doesn’t add up. … If you’re a bad guy and you do some­thing good, that’s an aber­rant event. But if you’re a good guy and you do some­thing bad, it’s a window to your true soul. As a sci­en­tist I just cannot accept that.”

DeSteno pro­posed a more flex­ible idea of human moral behavior. Instead of a scale bal­anced between good and evil, per­haps virtue is flanked by two opposing desires: what’s good for us now versus what’s good for us in the long-​​term.

With sup­port from the National Sci­ence Foun­da­tion, DeSteno studies human char­acter in the lab. For example, to explore hypocrisy, he asks par­tic­i­pants to judge the fair­ness of their own behavior and that of another in the same task. Even when the two behav­iors are iden­tical, par­tic­i­pants con­sis­tently judge others more harshly.

While Judah Rosen­thal ini­tially cannot fathom the idea of killing his mis­tress to pre­serve his own vir­tuous life, he even­tu­ally ratio­nal­izes it. We often judge others for their immoral choices, DeSteno said, but when faced with the same cir­cum­stances can we be cer­tain we’d act more honorably?

We assume someone who is sleazy is never going to be good,” he said. “We assume someone who is trust­worthy is never going to be bad and when they are, it sur­prises us.” But if we can accept a more vari­able idea of char­acter, we can under­stand “the forces that turn saints into sin­ners and cow­ards into heroes.”