The Four Functions are the four codes used by Qabalists to interpret the relationship between numbers, symbols, and other aspects of the spiritual world. The four functions are (1) Numeration; (2) Gematria; (3) Notarikon; and (4) Temurah. These four functions are used to decode the hidden truths of the Qabalistic tree of life.
In terms of Tarot, the Four Functions can help to understand the archetypes and symbols associated with each card, as well as the deeper spiritual meanings behind the cards. For example, the number associated with a card can be used to decipher the essence of the card, while Gematria can be used to identify specific correspondences to the card's attributes. Notarikon can be used to identify deeper symbolic messages associated with the card, while Temurah can help to unearth hidden connections between different cards within a Tarot deck.