IT’S AN INGENIOUS HYBRID—neither a jacket (softer, more comfortable, less intimidating) nor a pullover (the front opening guarantees easier on-and-off that doesn’t wreck hair or get you stuck in unbecoming positions). It is compassionate toward the body: covers the sensitive upper-arm zone, drapes the shoulders nonchalantly, disguises hips and belly when tied around your waist. Knot it under the bust for a cropped ballet-top effect (but no bare midriffs unless you’re eight years old). Don’t get a twin set. The cardigan’s color should look okay with what’s under it, but veer away from an exact match.
James Brudenell, seventh earl of Cardigan (1797-1868), was a lieutenant general who supposedly wore a knitted waistcoat during military campaigns. Notorious for having led the suicidal Charge of the Light Brigade during the Crimean War, he was initially welcomed home as a hero—hence the popularity of the eponymous garment. Later, doubts arose about his conduct during the ill-fated foray.    
His reputation has not sunk the sweater named after him. Cardigans, because they are unfussy and untrendy, have superior longevity. I’ve had three silk knit ones from J. Crew for about 20 years. Agnès B is famous for her classic black styles with tiny buttons, and I have a couple, but even the largest size tends to be tight on me. I also have a pumpkin cashmere that belonged to my mother. I rarely wear it but like to know it’s there.
My cardigan this summer, a light olive pima cotton with a v-neck and multiple buttons on the sleeves, is from Adam Lippes, master of the well-cut, high-quality knit (it’s five years old, and I don’t see any equivalents right now on, but there may be some when fall arrives. Meanwhile, probably has sales).
Put one in your tote, folded, if you’re going to the movies this summer. It gets cold in there.