Flusser on Ivy

...The 1950s are best remembered for the “gray flannel suit” worn by the conservative businessman. Now men were back to the natural-shoulder silhouette. As reported in Apparel Arts ‘75 Years of Fashion, “No style was ever so firmly resisted, so acrimoniously debated - or more enthusiastically received in various segments of the industry. Natural shoulder styling eventually became the major style influence. Brooks Bros., once a ‘citadel of conservatism,’ became a font of fashion as the new ‘Ivy Cult’ sought style direction. Charcoal and olive were the colors.”
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The Sack, or Brooks Brothers Natural-Shoulder, Suit

The sack, or the Brooks Brothers natural-shoulder, suit has been, for almost a century now, the backbone of American clothing. First popularized near the turn of the century, it was a silhouette characterized by a shapeless, nondarted jacket with narrow shoulders (which were soft and unpadded) as well as by flap pockets, a single rear vent, and a three- or four-button front. Designed large in order to fit many sizes, it was the first mass-produced suit and it looks it. After all, it was not called the sack suit for nothing.

Perhaps the biggest strength of the sack silhouette is also its basic weakness: it hides the shape of its wearer and takes away any sense of individuality. The reason it has managed to exist successfully for such a long period of time is simply that it appeals to the common denominator. Since it is so anonymous, it offends no one, enabling the wearer to walk into any environment and be acceptably attired.

For those seeking anonymity in their clothing, or wishing to hide an ungainly figure, this may be an acceptable style. But for anyone else, the sack-style suit is woefully inappropriate.
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The Button-Down Collar

The button-down collar was first introduced in this country by Brooks Brothers, patterned after the polo shirt worn in England. As explained earlier, the collar was originally fastened down in order to prevent flapping in the player's face during a match. This collar, unlike all others, is soft and meant to remain that way. It is without doubt the most comfortable collar and represents nothing less than the American spirit by producing a casual image so in tune with our heritage. It has been popular every decade since the twenties, and since its origins are definitely in sport, it is not considered a particularly dressy collar. Since it never lies exactly the same way, it offers an unpredictable buckling about the neck, thereby reflecting the wearer's individuality. It is a collar long associated with the Ivy League look and is especially complementary to the natural-shoulder suit. It is appropriately worn with tweed sports jackets and women suits. The Brooks Brothers original model remains the best version, for its points are long, permitting a "roll" that changes as the wearer moves. The button-down collar will accommodate a Windsor knot or a four-in-hand, and when worn with a bow tie, it projects the ultimate professorial image.

Source:

Alan Flusser, Clothes and the Man: The Principles of Fine Men's Dress, 1985