Yael Aflalo's story starts in Los Angeles. She had run her first label, Ya-Ya, from 1999, and then, in 2009, she launched Reformation. Porter described the mission as one "to recast ethical fashion as a desirable, stylish and contemporary proposition." Aflalo put the point of view her own way: "Our brand is all about reframing old-school concepts." The label describes its silhouettes as ones "that celebrate the feminine figure," and that is the part people want to borrow.

Here is what a Reformation dress dupe means in this edit. It is not the original and it does not pretend to be. These are pieces from other labels that share the details the original is known for: the square neckline, the fitted bodice, the linen sundress, the bias satin slip, the corset seam. Fashion writers have said the same thing about shopping this way. Bustle advises you to "pinpoint the design detail you feel best defines it," and I would start with the neckline.

The square-neck midi is the one I would begin with, and in mid-October it works with a cropped cardigan and tights. The Theory in blush is a stretch linen blend with pockets and a flared skirt, so it moves like a real dress. The Marcella Margot in black is a fitted jersey midi with a square scoop neck. The Monlicia Mel in ivory is 100% viscose with a pleated waist and the Julia Jordan in emerald is satin with a bow at the waist, both for evenings. For daytime, the Odd Muse in navy has a denim look and a pointed waist seam, and the 3.1 Phillip Lim in yuzu yellow is structured cotton.

Here is my test. Check that the bodice seams sit flat across the bust and that the straps are wide enough to keep the square neckline square. If the neckline bows when you lift your arms, put it back.

Linen is the fabric that decides whether a sundress looks crisp or limp, and the press has a clear opinion on what to look for. One fashion editor says to "rely on the breathable linen fabric, and look out for thoughtful design details like adjustable strap lengths and an elasticated back panel." That is the list I would carry into a fitting room.

The STAUD Ayla in olive has the square neckline, adjustable straps and a smocked waist, so it ticks all three. The Reiss Dorethea in orange is pure linen with wide straps and a softly flared skirt, and the Eileen Fisher Split V Neck in red is a sleeveless linen shift with a split collar and a center seam. The Dolce Cabo linen cotton midi in white has a scooped neckline, a button front and eyelet panels. In October I would wear any of these with a fine knit over the shoulders and flat boots.

Lining matters too. The same editor praised a linen dress because it "is fully lined to ensure it isn't sheer." Hold the skirt up to a window. If you see your hand through it, either add a slip or move on. Smocking at the back, as on the Petal & Pup Kayt, gives stretch without a zipper line, and the Point linen blend maxi in black keeps a clean crewneck line instead.

What I would skip: the V-neck maxi in black from DKNY or the tiered matty m. Louisa if you want the square neckline, since they share the fabric but not the neckline.

A slip dress is simple on purpose. One bridal stylist defines it as "a simple, unstructured silhouette that skims the bodice and is often made of silk or satin fabric, enabling movement throughout." Because there is so little to it, the cut does all the work.

The cut I look for is the bias. The Knot says it plainly: "The bias cut gives it a beautiful drape, so it lays perfectly and skims the floor as you walk." The AQUA lace-trim midi in chocolate brown has a drapey cowl neck and an asymmetric lace hem, which is the clearest match in this group. The AllSaints Irina in black has paneled seams and adjustable straps, and the Vince in black has crinkled satin with a V-neck. For fall dinners I would put either under a long wool coat with pointed boots.

Test it standing: the hem should hang level, not swing up at the sides, and the straps should adjust enough to set the neckline where you want it. Rust and burgundy read right for October. The Petal & Pup Cyprus in rust has a drapey cowl, and the AQUA lace-trim slip in burgundy has a lace-edged neckline.

What I would skip: the lace-trim Socialite in navy if you want a clean line, since the lace pulls it toward lingerie.

Corset seaming is a construction idea before it is a look. The seams run vertically, there is boning inside, and the top holds a shape on its own. That is the detail I would check before anything else, so turn the top inside out and look at the seam allowances.

The Miss Circle Tristyn in black has vertical corset seams and crystal straps, and the HOUSE OF CB Balconette in black has a square neck and a hook-and-eye front. The Lioness Capri in dark denim brings boned panel seams to a casual fabric, which I would wear with trousers and a trench. The JLUXLABEL Fenix is a strapless cotton and linen top, and the ALICE + OLIVIA Kim has paneled corset waist seaming under a collar, which suits office days.

Fastenings tell you a lot. A hook-and-eye front, as on the Joe's Jeans Femme and the EDIKTED Whitley, should lie flat and close in a straight row. A lace-up back, like the HOUSE OF CB Selma in white pinstripe, lets you adjust the fit after dinner.

What I would skip: any top where the seams curve but nothing sits inside them. It will look right on the hanger and slump on you.

Prints are where a look-alike can go wrong, because scale is hard to get right. Choose a ditsy floral with a small repeat and a soft color range, then check that the print matches across the front tie.

The Blu Pepper in brown floral has a tie-front bodice and an A-line skirt, a good one for October with boots. The Petal & Pup Kathleen in cream floral has puff sleeves and front ties, and the Ghost London Clarissa in mauve has an empire waist with a tie neckline. The Leota Adriana has a self-tie front and blouson sleeves in green and pink, and the Cinq à Sept Antonetta has flutter sleeves and a tiered hem in black floral.

Test the tie: pull it gently and see if the bodice gathers evenly or drags to one side. The tiered skirts, like the Avec Les Filles ruffle maxi, should hang with fullness at the hem and not at the hip. A cropped denim jacket takes the edge off any of them.

What I would skip: the Another Girl mini and the Show Me Your Mumu off-shoulder wrap if you want the midi length and a covered shoulder for cooler days.

I would start with the square neckline, since it is the detail everyone recognizes. Then I would check the fabric, the lining and the seams in that order, because those are what make a dress read well.

For October I would pick the blush Theory or the navy Odd Muse for work, and the bias satin slip for dinners. Then I would add a corset-seamed top to wear with trousers. A look-alike works when it shares the idea: a founder in Los Angeles in 2009 wanted dresses that were feminine and in charge, and that is a good brief for any closet.