In 1925, when René Lacoste won both the French Championships and Wimbledon, he wore a starched white shirt with buttons extending all the way down the front and sleeves reaching to the wrists. In 1926, he won the United States National Championship wearing the same shirt but with its sleeves cut short: a daring evolutionary step toward an archetype of sportswear. In 1933, Lacoste went into business with a knitwear manufacturer to mass-produce la chemise Lacoste, a short-sleeved pullover with a turndown collar, three buttons on its placket and a breathable piqué-cotton body. Ads extolled its suitability not just for le tennis and le golf but also for la plage (the beach): not just for athletic exertion but for general leisure. The shirt was not rigid, but there was a rectitude to it. It promoted physical comfort while adhering to social strictures. The line from there to casual Friday runs fairly straight.

Lacoste once told People magazine that he derived inspiration from seeing one of his fancy friends, the fifth Marquess of Cholmondeley, take the court in the shirt he wore to play polo: ‘‘A practical idea, I thought to myself.’’ It is true that the polo shirt as we know it originated on the polo field, but it is also true, and telling, that the game’s name has attached itself to many other garments. If you check inside the collar of a Brooks Brothers oxford-cloth button-down, you will see it declared ‘‘the original polo shirt.’’ When you flip through 1940s newspapers, you will find boys’ knit-cotton crew necks promoted as ‘‘polo shirts.’’ What an American calls a turtleneck sweater, a Briton calls a polo-neck jumper. A camel’s-hair coat was, in the 1920s, a polo coat. The brand name Polo Ralph Lauren first materialized on a label, paying quiet tribute to customers’ Gatsby streaks, in 1967; Lauren did not hitch his pony and rider to a polo shirt until 1972.

The connotations of polo are elite but not effete. What is a polo player if not an aristocrat fused with a cowboy? And yet a ‘‘polo shirt’’ sounds somehow more approachable than a ‘‘tennis shirt,’’ probably because the equestrian game exists at such a ludicrous remove as to seem no more substantial than a mirage. The oddities attendant to the status of reappropriated symbols are delightfully rich. Ralph Lauren, born in 1939 as Ralph Lifshitz, has frequently been compelled to defend his trademark against the United States Polo Association, founded in 1890 as a sports organization. Entering the rag trade with its U.S. Polo Assn. line in 1981, the group aroused the ardent curiosity of Lauren’s legal team. Lawyers have met with limited success in arguing that polo (the institution) endeavors to ride the shirttails of Polo (the upstart) by selling shirts emblazoned with twice as many horses (and at half the price).

Meanwhile, Lacoste remains the brand emblematic of branding itself. Descended from the player’s personal insignia, the famous crocodile is sometimes claimed as the first commercial logo designed for display. Though that distinction more likely goes to the diving girl of Jantzen — the suit that, to believe its slogan, ‘‘changed bathing to swimming’’ in the 1920s — both symbols emerged from the same pool of ideas. The years between the wars marked the advent of purpose-designed sportswear and its slippage into the mainstream, guided by the new prestige of youthful vigor. Advances in technology abetted shifts in standards of decorum, and now here you are, wearing yoga pants out to dinner.