I Ching, Yijing or Zhou Yi
"Oracle of the moon": © 2000 LiSe
Some players could use their memory. But intuition is also part of it. It is a subliminal reservoir of knowledge, experience and intelligence, but it is also connected to a more universal mind, and anything emerging from there seems like chance, luck, clearsightedness or assisting gods or angels.
Chance and luck - magic.
This is why oracles 'work'
and why it was inevitable that cards acquired the function of oracles.
The first decks (or packs) of playing cards appeared in the 9th century during Tang-dynasty China.
The Tarot pack was invented in northern Italy in about 1425. A plethora of references to the cards, from Italy in the XV century testify to their use as instruments in a special kind of card game. None associates them with the occult, and only one very dubious one hints at a use of them to read individual characters. It was not until the XVIII century that the use of them for divination became widespread in Bologna and France. Their association with the occult originated exclusively in France; neither it nor their use in fortune-telling was propagated in print until 1781.
The basic rules first appeared in the manuscript of Martiano da Tortona, written before 1425. Tarot games originated in Italy, and spread to most parts of Europe. They are played with decks having four ordinary suits, and one additional, longer suit of tarots, which are always trumps, a playing card of the suit chosen to rank above the others, which can win a trick where a card of a different suit has been led. Tarot games may have introduced the concept of trumps to card games. Trump: "a valuable resource that may be used, especially as a surprise, in order to gain an advantage".
Tarot decks did not precede decks having four suits of the same length, and they were invented not for occult purposes but purely for gaming. In 1781, Court de Gébelin published an essay associating the cards with ancient wisdom, the earliest record of this idea. As a result, tarot cards have since been used for cartomancy and divination as well as gaming, although nowadays fortune-tellers tend to use specially-developed tarot decks rather than those used for games. The Rider-Waite tarot has been inspired by Waite's connection to the Golden Dawn, with the result of innumerable mystic symbols on cards which used to have just quite simple images.