A trigram is three lines. There are eight of them (bāguà, 八卦). Every one of the 64 hexagrams is an upper trigram sitting on a lower trigram. If you can recognize the eight, you can identify a hexagram without flipping through a book at random.
This is the small alphabet under what is the I Ching. Casting still produces six lines; trigrams are how you read the stack. See coin method.
The Eight, Bottom to Top
Lines are read from the bottom. Yang is unbroken. Yin is broken.
Qian ☰ (乾) Heaven. Three yang. The Creative. Strength, initiating force, the sky as verb. In the later family scheme: the father.
Kun ☷ (坤) Earth. Three yin. The Receptive. Yielding, carrying, the field that makes the seed possible. The mother.
Zhen ☳ (震) Thunder. Yang at the bottom, yin above. The Arousing. First movement, shock, the startle that begins a season. Eldest son.
Kan ☵ (坎) Water. Yang in the middle. The Abysmal. Danger, the gorge, heart in the dark, work that has to go through. Middle son.
Gen ☶ (艮) Mountain. Yang at the top. Keeping Still. Stopping, the ridge, a back that does not move. Youngest son.
Xun ☴ (巽) Wind / Wood. Yin at the bottom. The Gentle. Penetrating, gradual, the influence that arrives by weather rather than by blow. Eldest daughter.
Li ☲ (離) Fire. Yin in the middle. The Clinging. Clarity, dependence on what it burns, light that needs a wick. Middle daughter.
Dui ☱ (兌) Lake. Yin at the top. The Joyous. Openness, exchange, the mouth of the valley. Youngest daughter.
The family labels are a later mnemonic, not a gender rule for your life. Use them if they help you remember the lines. Drop them if they make the trigrams into a soap opera.
Lower and Upper: Place Matters
The lower trigram (lines 1–3) is often read as the inner condition, the starting position, the part already underfoot. The upper trigram (lines 4–6) is often read as the outer condition, the field, what the situation is moving into.
Water below Fire is a different hexagram from Fire below Water. Same ingredients, different cooking. When you identify a cast, name lower then upper: “Mountain below Fire” is Hexagram 56, the Wanderer. “Fire below Mountain” is a different figure.
This is also how nuclear hexagrams are built: they take the inner four lines and recast them as two trigrams. Learn the eight first.
Trigrams as a Daily Practice
You do not need a full cast to use the eight. Look at a day and ask which trigram names the weather: is this a Thunder morning (something already started with a jolt) or a Mountain morning (the useful act is not moving)? That is a naming exercise, not a forecast.
The eight also appear on the [Later Heaven] bagua used in some feng-shui and Nine Star Ki contexts. Those applications remix the trigrams into space and direction. Keep the I Ching reading and the house-compass reading labeled as different jobs.
Frequently Asked Questions
Are trigrams the same as hexagrams? No. Trigrams are three lines (8). Hexagrams are six lines (64).
Do I memorize the lines or the pictures? Both. The picture (Heaven, Lake) is faster in conversation. The lines are what you actually cast.
Why do some sources list different attributes? Two thousand years of commentary. Stick to image + structural quality. Ignore the kitchen-sink correspondences until you can identify a hexagram by eye.
Is this binary? Each line is a bit. Eight trigrams are three bits. The rhyme is real; the metaphysics is optional. See I Ching and binary.