In 1854, during the Crimean War, James Brudenell, 7th Earl of Cardigan, led the Charge of the Light Brigade at Balaclava, and the cardigan took his name. The story goes that British soldiers already wore a knitted wool coat with the basic shape of the modern one, and the Earl's fame did the rest. A garment named after a battlefield has ended up as the softest thing on an October hanger.

Two women made it ours. Coco Chanel brought the cardigan to women in the 1920s, supposedly because men's sweaters pulled over the head wrecked her hair. In the 1930s Pringle of Scotland, under designer Otto Weisz, invented the twinset, a matching short-sleeved pullover and buttoned cardigan. The cropped cardigan is that idea trimmed back to the waist, where it meets a high-rise skirt or trouser and the outfit suddenly has a line.

Cashmere is the place to begin, because a short hem only works when the knit is fine enough to sit flat. I would take the navy Allude crewneck for the plainest, most useful version, and the beige Allude with ribbed trim if you want a boxier shape. The Khaite Nora is short-sleeved and black, with fine buttons, which makes it a good one to wear alone in a warm office. Arch4's Rome in orange has puff sleeves and a ribbed hem, a loud piece in a quiet fabric, and the Sablyn Jolie in a pink-to-plum ombre is the soft, brushed one.

For cooler days I would look at the Reformation Caspia in cream, slim with a ribbed trim, or the espresso Joe's Jeans Dani under a wool coat. Favorite Daughter's Rebecca is styled with high-waist trousers, which is the right instinct. Button every button and wear it as a top, then check that your shirt hem does not peek out below.

Thin knits behave differently from cashmere, and the first test is the hem. Hold the cardigan against your natural waist in the mirror and see whether the ribbing lies flat or flares. In a fine gauge it should lie flat, which is why this group is the one I would wear under a blazer.

Theory's Crop Crew in black is 100% merino with ribbed trim, a clean, close option for work. Toccin's Zoe in jet is fitted and cropped at the waist, and the SKIMS ribbed jersey cardigan in obsidian is a stretch version that stays put when you move. R13's merino cardigan in charcoal has a deep V, a gathered hem and pearly buttons, the one with a little attitude. Chinti & Parker's wool and cashmere blend in chocolate is mid-weight and boxy, so it needs a slim top underneath.

For something softer, French Connection's Babysoft in porcelain cream is slim and fine-ribbed, and Loulou de Saison's Heike is pure brushed cashmere with raglan sleeves. Pearl-buttoned or plain, any of them looks right over a silk camisole and high-waisted trousers, the old twinset idea in a shorter cut. Chanel wanted a layer she could pull on without ruining her hair, and a button front still does that.

What I would skip: anything in thin jersey that clings at the hem, since a cropped line shows every ripple.

Check the buttons, too. Do them up and sit down, because a fitted cardigan should not gape across the chest when you reach for a bag.

The polo cardigan is a younger idea than the twinset, but it comes from the same wardrobe: a knit that does the work of a blouse. The collar is what changes the picture, so the test here is how it sits against your neck when the cardigan is buttoned to the top.

COS makes a coral cotton polo cardigan in a shrunken silhouette, short-sleeved and easy under a blazer in October. Maje's navy polo has removable gingham trims, so it can look prep or plain. Alice + Olivia's Dollie in heather gray has a removable white collar and cuffs, hitting at the high hip. Isabel Marant Étoile's Zoe is cream with a pointed collar, a fair isle yoke and gold buttons, the most decorated of the group.

Calle del Mar's cropped cashmere zip-up in speckled blue has a wide ribbed collar and patch pockets, which makes it the sporty one. THE GREAT. adds a crochet-trimmed collar in marled brown. For summer-weight, LE BOP's crochet polo in black has scalloped edges, and Varley's Gaelle is a chevron-stripe cotton polo with elbow sleeves.

Wear a collared one with a high-waisted pair of pants or a pleated skirt, tuck in whatever is underneath, and let the collar be the only detail. Tall boots pick up the preppy feel.

What I would skip: stacking a collared cardigan over a collared shirt, because two necklines compete.

Texture asks for more care at the waist, because a thick hem sits away from the body. Put your hand under the hem and see whether it ends where your trousers start. If there is a gap, the proportion will look chopped, so pick the ones with a ribbed band.

Doen's Danae is a cream cable-knit in 100% cashmere, which is as soft as texture gets. Khaite's Niels in light gray is a chunky marl with gold-tone buttons, made from cashmere and silk. Ruadh's Cadogan in chartreuse has balloon sleeves and chunky rib, and Haven Well Within's shaker-stitch cardigan in island sand heather is designed to hit above the hip.

On the preppy side, Polo Ralph Lauren's cable cardigan in cricket cream has green whipstitch trim and mother-of-pearl buttons, and Rowing Blazers' Donegal cable knit comes in a flecked beige with a small sheep on it. Good American's Chunky Knit is heather gray with drop shoulders and wide sleeves. Sablyn's Jolie cable in hunter green is cashmere again, in the deepest autumn color of the lot.

Pair one with a fitted tee or a thin turtleneck and a high-waisted straight leg. Keep the volume in one place: if the sleeves are wide, the pants should be slim.

What I would skip: layering a chunky crop over a loose, long shirt, since the bulk ends up in the middle of the body.

A pointelle knit is a pattern of tiny holes, and the test is simple: hold it to the light. The holes should be even and small, and the cardigan should still feel like it has some weight to it. Stripes need a different check, because they should line up at the button band.

Cara Cara's Louise is a navy and white wavy stripe in cotton with a scalloped hem. La Ligne's Fine Line Mini Marina is a cerulean and ivory collared cotton cardigan, and LE BOP's Mara is a sky multi-stripe in the same fiber, with a button placket. Reformation's Clara Stripe is dark pine and cream, and unlike the cotton ones it is cashmere, which suits October.

The pointelle side is brighter. Joe's Jeans makes the Dani in sunshine yellow with ribbed trim, L'AGENCE's Ninette is a black polo with grosgrain ribbon trim, and LoveShackFancy's Nadiya in candy floss pink has scalloped trim. Barefoot Dreams' pointelle cardigan in umber has coconut buttons and a relaxed, boxy crop.

I would wear a striped one with straight jeans and loafers, and keep the pointelle ones for skirts. A yellow knit over white trousers is the easiest daytime look going.

What I would skip: a striped crop over a striped top, which makes a busy waistline rather than a defined one.

Begin with the fabric you will wear most. If that is a black or navy cashmere crewneck, buy it, and pair it with the high-waisted pants you already own. A cropped cardigan lands at the natural waist, and without a high-rise bottom it can look accidentally small.

Then add a second piece with a detail: a collar, a cable, a stripe. Button it up and wear it as a top in the first week of cold weather, and open over a tucked tee when it warms up.

The Earl of Cardigan probably never imagined his name would end up on a waist-length knit. I think he would approve of the buttons.