Updated: Oct 13, 2021
The short answer is: no one can tell you definitively, and no. But let's dig deeper.
Before being able to answer how tarot cards work, we need to define what "working" actually means. In other words, what are tarot cards supposed to do?
What can tarot cards do?
You would probably guess that they are for divining the future, or at least for trying to do so. That's because of how tarot cards and other means of divination (think crystal ball and magic mirror) are depicted in pop culture. And, to be fair, many readers do use tarot cards to try to peek into the future, and some are successful at doing so.
The reason that tarot cards can sometimes manage to "show us" the future is because their actual purpose is to show us the unbiased truth of things, allowing us to see the bigger picture. (Note: Readings can be biased and thus skewed when the reader's question is muddled by strong interfering emotions.) Often, when we look at the bigger picture, it becomes obvious what the most likely outcome will be. The farther out you zoom, the more you can see where paths converge and in which directions they point. However, it is important to note that the future is not set in cement. There is always potential for us to leave our mark on it until it becomes the present moment itself. For that reason, future predictions can never be more than just that: predictions. They do not guarantee an outcome.
Knowing all this, it is clear that using the lens of the tarot is most beneficial when we point it at the past and at the present. From that viewpoint, we can see patterns of thought and behaviour emerge. We can see what harms us, what benefits us, what we'd like to change, and how we could potentially change it. We can see ways of bending and moulding the path we currently walk so that it ripples into the future, seamlessly aligning itself with our innermost desires. Why try to predict the future when instead you can heavily influence it?
How do tarot cards work?
So now that we know what tarot cards are capable of, the big question returns: how do they do it? There is not yet a scientifically proven answer to this question, and so I can only tell you what is generally believed and what I myself believe.
Some people believe that the movement of the tarot cards is physically manipulated by spirits, gods, ancestors, spirit guides, or other entities. Others believe that these entities indirectly guide us to the correct tarot cards through signs, visions, gut feelings, or other intuitive responses.
Some believe (and I fall into this camp, but I keep an open mind since I cannot answer the question with full certainty) that the Universe realigns itself perfectly in order to respond to questions or vibrational calls. Instead of it being a God or a spirit redirecting things, it is one big flawless machine, built in such a manner that it obtains precise outcomes by following precise laws. Such as what goes up must come down, what is asked must be answered.
When using tarot cards while asking a question (even one as vague as, "what do I need to know right now?") our bodies move the cards -- shuffling, cutting, and picking them -- in a way that perfectly responds to the question. Our bodies unconsciously react in this way because they are a part of the Universe, and the Universe is aligning itself to perfectly answer our question. Whether you believe that the Universe as a whole is sentient or not, the Universe falls into the definition of "entity." And so, in a real roundabout way, an "entity" is indeed directly or indirectly affecting the physical movement of the tarot cards in response to a question... That "entity" just might be your own unconscious mind. All that to say, it doesn't really matter how they work, all that matters is that they do. The only case in which the "how" would matter is if tarot cards were dangerous. So let's move on to that part of the question.
Are tarot cards dangerous?
Again, the short answer is no. However, like any tool, it depends how they are wielded. A hammer is not dangerous unless the intent behind it is.
On a physical level, tarot cards could only be dangerous if they were used to give someone a paper cut. Other than that, they remain small rectangles of card stock, harmless by nature. So how could they potentially be dangerous, then?
Some people believe that if you carry a lot of fear while working with any divination tool, including tarot cards, then you will unknowingly attract a malevolent being, entity, or spirit. I cannot say that I believe that to be true, but I will still not encourage anyone to work with a tarot deck while carrying a lot of fear. I believe that the worst that can happen in that case is that the fearful reader walks away even more fearful, or fails to receive the bigger-picture messages in seemingly scary cards such as "Death" and "The Devil."
If you want a clear, unbiased answer, then your question must come from a place of clarity and of impartiality. Fear can quickly get in the way of what should be a sharp intention.
Another way in which tarot cards can be dangerous is if they are used to infringe on others' free will. For instance, asking to see someone's private thoughts and feelings through the cards. That would essentially be spying, since it involves secretly gaining access to information that you are not meant to have access to. However, this is more a matter of ethics than it is of danger. There are plenty of readers that do not hesitate to ask such invasive questions. This could wind up being dangerous, or simply undesirable, in the long run if the knowledge that is gained leads to actions that ultimately change outcomes for the worst.
The final way in which tarot cards could be perceived as dangerous is if they are poorly interpreted. If you are reading for yourself and you misinterpret the cards that you see, you could make decisions that go against the advice that the tarot cards were attempting to offer. This is really only possible when fear, intense emotions, or certain beliefs cloud your view. Since the Universe aligns itself to perfectly answer your questions (as long as they come from a place of clarity and of impartiality), it will deliver to you the exact cards you need to see in order for you to personally understand the message. That is to say, it is not possible to pick a "wrong" card, so if you are having trouble interpreting the cards, maybe make a note of them, step away for a bit, and come back to them when you have a clearer head.
When reading for others, misinterpretation of the cards can have a much bigger impact. People tend to reach out to tarot readers for answers in times when they are most vulnerable. In their vulnerability, they often take the tarot reader's words with great weight. If a reader gives unhelpful advice during a reading, it could lead to unfavourable outcomes for the person applying the advice. In general, it is good practice to be thoughtful and diligent when reading tarot cards for someone else.
All in all, tarot cards are a tool and, like any tool, they must be used with great care, respect, and with clear intention. It is a good idea to ask yourself what your ethics are when it comes to tarot reading, especially if you plan to read for other people, and even more so if you plan to read the cards in a professional setting.
As long as your intentions are good and pure, there is no reason to fear tarot cards. If you find yourself interested in them, but deep down you are afraid of picking up a deck, perhaps you could benefit from speaking to a seasoned reader about their experience with the cards. Of course, having your cards read by a professional and asking questions about the process is a great way to overcome fear of the unknown. Reach out to your local psychic. Odds are, you will be surprised at what you learn!