Mary-Kate Olsen. I don't even know where to begin.

Can Mary-Kate really be the incomparable Ashley Olsen's twin sister? They may have the same genetic code, but Mary-Kate certainly does not have her sister's prodigious dramatic gifts. For eight years on Full House, the pint-sized duo shared the role of Michelle Tanner. But, despite their identical outward appearance, it was easy to tell which sister was Michelle at any given moment. I cringed whenever Mary-Kate would appear on my TV screen, her clumsy, ham-fisted portrayal of the littlest Tanner devoid of all nuance and depth. And her incompetence was laid all the more bare by her sister's mastery of the role.

The twins' post-House work only widened the gap. Over the course of countless children's sing-along videos, TV movies, and such sitcoms as Two Of A Kind and So Little Time, it's been made painfully obvious who's got the chops and who doesn't. Ashley is George Michael to Mary-Kate's Andrew Ridgeley. She's Daryl Hall to her sister's John Oates.

Yes, it's clear that Ashley Olsen is the one with the true talent and personality. She is the majestic airship hovering in the sky, while Mary-Kate is the oppressively heavy, rust-encrusted anchor to which that airship is cruelly tethered, preventing it from ascending high into the firmament. Ashley could be another Hepburn, another Streep, if not for the cumbersome ballast that is Mary-Kate.

Examples of Mary-Kate's incompetence are as abundant as blades of grass. Space limitations force me to restrict my examples, yet the handful I have selected are nevertheless damning:

Mary-Kate lacks charisma. That elusive quality is vital to a performer, yet Mary-Kate is almost completely devoid of it. With her vanilla features and expressionless, fish-eyed gaze, one must wonder why this singularly untalented waif was ever placed before a camera. Case in point: In 1995's "The Case Of The Sea World Adventure," from the direct-to-video children's mystery series The Adventures Of Mary-Kate And Ashley, Mary-Kate delivers such lively and toothsome lines as, "The pearl necklace must be in that bucket of bait... yecch!" with about as much élan as a TV agribusiness reporter delivering the day's livestock quotes. If she required guidance or inspiration, she need only have turned to Ashley, whose unmasking of the jewel thief was as suspenseful as the climax to any classic 1940s film noir. "Trenchcoat Twins," indeed.

Mary-Kate's diction is poor. Another acting skill so vital, yet so utterly lacking in Mary-Kate, is clear enunciation. Her high-pitched, reedy, mealy monotone seems oddly out of place coming from her ponderous maw. Yet, like the call of the shrike, it pierces the eardrums and inspires profound irritation. This paucity of resonance applies to her singing voice, as well, and is readily apparent in the girls' 1994 recording, "Brother For Sale." No amount of studio wizardry could conceal the cracks in her off-key, phoned-in "singing." It was clear she didn't believe in the song. Meanwhile, Ashley's hearty vocals and peerless phrasing were reminiscent of a brilliant prodigy of yesteryear, Judy Garland. Whereas Ashley sang from her diaphragm, Mary-Kate's voice seemed to emanate from a tinny transistor radio with a dying battery.

Mary-Kate is not as good-looking as Ashley. Mary-Kate's disheveled rat's-nest hairdo looks as though it has never experienced a comb or shampoo. She never seems to have a straight part, and the fussy little barrettes stuck randomly throughout her hair only accentuate its unruliness. Her wardrobe, from To Grandmother's House We Go to Billboard Dad, has always been tacky and dowdy, inspired by some bizarre Schoolmarm Chic trend that exists only in her head. By contrast, Ashley is a heavenly apparition. Her strawberry-blonde mane falls in glossy ringlets, her well-scrubbed skin radiates a golden, healthy glow, and her erect bearing exudes a sylph-like grace, giving her a larger-than-life appearance despite her diminutive frame. Her fashion instincts are as unerring as Mary-Kate's are clueless.

Mary-Kate could also stand to lose a few pounds.

I say these things not to humiliate Mary-Kate. It is altogether likely that the girl possesses talent—just not in an entertainment-industry capacity. Perhaps, after extensive training and a long probationary period, Mary-Kate could make a serviceable cashier, nursing-home orderly, or cafeteria worker. Or maybe she could serve as an assistant to Ashley—a star of her sister's magnitude surely needs someone to answer her fan mail, clean her trailer, and fetch her bottled water.

I fear that if Mary-Kate is not forced to relinquish her partnership with Ashley, the duo will eventually go down in a blaze of mediocrity. Their careers will become mired in a bog of formulaic sitcoms, forgettable TV movies, and mindless, mercenary merchandising peddled to the lowest common denominator. And that will be a real shame, because the girls have so much to offer. Well, Ashley does.

Mary-Kate, please do your twin a favor: Set her free to soar like the eagle she is. Only when she is loosed of the sisterly bonds that hold her down can Ashley assume her rightful place in the pantheon of greats.

This full house must be divided, or it will not stand.