There are four suits in the Tarot, as well as the Major Arcana. Each of these suits correspond to a given element: Earth, Air, Fire and Water. The suits are interpreted differently depending on the element they belong to. So Earth tends to focus on family and money issues, whereas Air focuses on communication and the intellect.
The four elements are part of ancient teaching. For a long time, it has been believed that material life is made up of these elements, and without them there would be no world and no life on it. It makes sense when you think about how without Earth there would be no planet, without Water we could not drink and nothing could grow, without Fire there would be no Sun and so no life, without Air we could not breathe.
Everything in our material world belongs to one or more of these elements. So a book could belong to Earth because of its physical presence, but it might also belong to Air since it is passing on knowledge.
Each element can be active or passive, as they are part of the overall principle of polarity which is strongly emphasised within the Tarot. We have, for example, the polarities of the High Priestess and the Magician, the Emperor and the Empress.
