The element
Fire
The science
Fire is not a substance. It's an event. What we call a flame is combustion, fuel and oxygen tearing into each other fast enough to throw off heat and light, and the glow you see is gas so hot it shines. The wood doesn't disappear, it changes hands, leaving carbon dioxide, water vapor, smoke, and a little gray ash where the structure used to be.
It needs three things at once, and old hands call it the fire triangle: fuel to burn, oxygen to feed it, and enough heat to start and keep the reaction going. Pull any one of the three and the flame dies. That's the whole logic of every way we put fires out. Water steals the heat. A blanket or foam smothers the oxygen. Cutting a firebreak takes away the fuel.
Push the heat high enough and the flame stops being ordinary gas. The atoms shed their electrons and you get plasma, the fourth state of matter, the same stuff the sun is made of. So the small candle on your table and the star that lights the whole sky are the same trick at different sizes.
A few honest notes. Flames point up because hot gas is lighter than the cold air around it and rises, which is why a candle in zero gravity burns as a slow blue sphere instead of a teardrop. The color tells you the temperature, deep red is cooler, blue and white are hotter. And fire is the only one of the four old elements that isn't a kind of matter at all. It's matter caught in the middle of becoming something else.
The meaning
Fire rules Wands, the suit of will and want and the first move. When Wands come up, the question isn't what's true, it's what wants to happen, what you're reaching for, what's already lit in you whether you've named it or not. This is the suit of the hand before it knocks on the door.
Its temperament runs hot and quick. Fire is the spark that gets you out of the chair, the yes said before the head catches up, the work that feels like play because you forgot to be tired. At its best it's warmth, a candle for someone else's cold room, a forge that makes a useful thing. It's the part of you that creates instead of only watching.
Too much and it burns the house it was meant to heat. Fire with nothing to feed on eats whatever's near, and you'll know it as anger that scorches the wrong person, a passion that flares and goes gray by morning, a wanting so loud it never lets the rest of you speak. Too little and you're cold, drifting, the pilot light out, plenty of plans and no match.
So when Fire shows up in a spread, sit with it a minute. Ask what you're actually burning for, and whether you've given it good fuel or just thrown your whole self on the pile. The flame isn't asking to be put out. It's asking to be tended.