"He who lives, while he is living, does not see himself live," wrote Luigi Pirandello. "If one can see his own life, it is a sign he is no longer living it."

People want to define themselves, he adds, to give their lives form and structure. But "to define is to kill." Those who see through the forms imposed on them, he says, are truly free.

When he began writing, Pirandello vowed never to pen a play. They merely illustrate something larger and "diminish and spoil" what they represent.

Everything's locked in a form - acts and scenes and moments - and predetermined. But what if the characters burned the script, banished scenery, and improvised their lives? If they could "free the stage from the eternal pose," the true story would emerge.

Tonight is about a Neapolitan family who come to Sicily and offend the locals with their lively manners. Sternest of the latter, Rico Verri, falls in love with Mommina. But he's so jealous of her previous life he locks her in a room (a metaphor for Pirandello's cage of form), and she wastes away.

Although a director, Doctor Hinkfuss, promises to do away with the author and his text, he grafts a new form onto the story, and the characters finally rebel.

The tactic's the opposite of Brecht. Instead of exposing theatrical illusions, the characters in Tonight punch through them to a deeper reality.

In theory. Tonight premiered in 1930, as part of Pirandello's trilogy of plays about theater. Today's audiences, conditioned by decades of Brecht, know that even the improvisations have been rehearsed. And the "reality" - of actors interrupting a scene or the director shouting orders - is yet another illusion.

Tonight is rarely performed and, because it's so quirky, has never had a good track record. Some speeches do go on, and the device of characters wanting to play themselves takes its sweet time.

UCSD's production is slow to start. The invasion of the characters, dressed like refugees with suitcases, and the Doctor's long disquisitions make for squirms in seats and iPhones blinking on. The acting in the beginning, which should feel spontaneous, even radically so, is the most mechanical - especially the badly timed, scripted shouts from the audience.

Gabor Tompa rushes in where most directors fear to tread (his Woyzeck at UCSD a few years back was excellent). Some scenes verge on falling apart, others lock into rigid form, then flip into smoothly flowing sections, as if happening "live."

He thrives on the interplay among the various levels. The frequent interruptions annoy so much they force the audience not only to improvise its role, but also to want the real story all the more.

The cast must perform mirror-like, shifting from acting to seeming to act, to not at all. Most pull it off. Two do much more.

The cuckolded Sampognetta is scheduled to die. The actor playing him, called Old Comic Actor, has so identified with the role that he can't: the mishmash he enters, with his guts falling out (literally), hasn't prepared the audience for a death scene. So he describes how he would have done it with such feeling that the actors weep.

But who, at this point, are they? The story's characters? The actors in the story playing them? UCSD's? All lines blur in the presence of William Hodgson/Old Comic Actor/Sampognetta's hilarious and deeply moving plight.

Katherine McGehee concludes the evening with a long, aria-like scene. She plays "Leading Actress," who is playing Mommina. Gray-haired, gaunt as Samuel Beckett, she's been locked in a room with her children for four years. She recalls the glory of the theater and begins to sing, with a near-operatic voice, Il Trovatore. The strain takes her life.

Is McGehee acting? Improvising the scene? Is she scripted, rehearsed? Who cares! Her combination of hyper-illumined reverie and agonized entrapment break through all the "theatrical" contraptions and counterpoints and reach that place, Pirandello promised, where she "lets loose" the life within her.

Mandell Weiss Theatre, UCSD, playing through March 2.