Why do card games involve imperfect information?

Card games involve imperfect information because they exploit the physical design of playing cards, which are identifiable from only one side. Consequently, each player can see only the cards they hold, while the cards held by opponents remain hidden.12

This structure creates a state of "past imperfect information," where the initial distribution of cards is randomized through shuffling. As the game progresses, players use observation—such as tracking bids, discards, and trick play—to deduce the distribution of the remaining cards, effectively turning the experience into a game of increasing information.1

While this is a common feature, it is not universal; some games, such as certain varieties of solitaire, involve dealing all cards faceup, which classifies them as games of perfect information. In contrast, games like poker remain classic examples of imperfect information because the hidden nature of the cards forces players to make strategic decisions without full knowledge of the current state of the game.12