Tarot

[Just_Me]

My understanding is that the Tarot represents several slightly different forms of tool used in divination, almost always taking the form of a "deck" of "cards" or "tiles." The exact method of using them for divination probably varies as much or more than the myriad methods of "divination" that exist in the real world. However, when considering them in the context of 40k it is important to recall that not only do actual legitimate psychic abilities exist but that prediction of the future is possible (if not exactly precise).

At the most basic level it probably takes the form of a set of plain old cards, not much different from what we have in real life. Most people using them at this level probably get about the same accuracy as we would (i.e. not much to none). When used by a psyker with some latent ability for divination they probably act as a medium for information, the psyker's talent manifesting through them to result in something meaningful, though due to the allegorical nature of the cards there is probably still a lot of room for interpretation. Both of the above represent their use by mundane/untrained individuals, in the hands of one trained and aware of their own psychic abilities they are used much more intentionally and probably also have the role of a focusing tool for their concentration. They still act primarily as a medium rather than a mechanism for prediction but because the dealer is aware of what they are doing and probably versed in interpretation the results are more reliable and accurate, though still not exactly precise.

In their most "evolved" form we have accounts of Tarot decks whose card/tiles are laced with or made of a psi-active or psi-reactive material so that they are far more responsive to the user's psychic abilities and/or the user can actively channel their abilities through the tiles. These are probably rare and most likely far more effective.

The exact role that the Emperor himself plays in this process is open to interpretation, both in-universe and to us looking in from the real world. I'm sure there are psykers who take a clinical view and attribute the effectiveness of the Tarot purely to their own abilities while others profoundly believe that every message from the Tarot is a divine message from the Emperor, not to mention a host of views in between. Personally I'm inclined to believe it is a little of both, sometimes the Emperor DOES reach out and use the Tarot as a medium to convey information, even to mundane users.

Of course, other methods of predicting the future have been observed in other factions who must necessarily use them independent of the Emperor. Rune-casting among the Eldar is perhaps the best example of this. Chaos sorcerers have been known to use a vast host of (usually unpleasant) divining techniques, though the intervention of Daemons and the Dark Gods themselves generally just further confuses the matter. After all, at worst the Tarot may just be WRONG, a Daemon/Chaos God might be ACTIVELY trying to give you misinformation for its own purposes. Or to screw with you. Because, you know, it can.

[Katharon]

If you want to see a decent representation of the Tarot being used in Wh40K books, check out "Cadian Blood." But yeah, the Tarot cards are made from materials that are able to be psychically manipulated - so that by channeling the warp and the Emperor's guidance the user can determine future events. The clearness of a reading seems to be determined by the power of the psyker in question and whether or not the warp is screwing with him/her.