Played with a pack of 52 cards, consisting of thirteen cards in each of four suits (Law 1A); The suits rank downward in the order spades (♠), hearts (♥), diamonds (♦), clubs (♣) (Law 1A); The cards of each suit rank downward: Ace, King, Queen, Jack, 10, 9, 8, 7, 6, 5, 4, 3, 2 (Law 1A)
Source: Law 1, Law 2 — American Contract Bridge League — Laws of Duplicate Bridge
Why people argue about this
People often assume that in Duplicate Bridge, each player must use exactly 13 cards from their dealt hand throughout the entire deal, which they think is a strict requirement for every card played. However, the actual rule states that players can discard or re-shuffle up to three cards during their turn if they choose, meaning it's not mandatory to use all 13 of your dealt cards at once.
