San He and Liu He: What 'Same Affinity Triangle' Means

By Mithila Labs

"Same affinity triangle" is shorthand for two distinct systems from older Chinese astrology: San He and Liu He. Both feed directly into the wording on this site's compatibility pages.

San He: the trines

"Three harmonies." The twelve animals split into four groups of three, each spaced four years apart:

Two animals from the same group are "in a trine" — that's the source of any "same affinity triangle" note on a compatibility page. The four-year spacing is the mechanism: animals that distance apart in the cycle tend to move at a similar pace even when their surface personalities differ.

Liu He: the six pairs

"Six harmonies" — a separate, arguably older system. Instead of grouping by shared rhythm, it fixes six specific two-animal pairs, sometimes called "secret friends," where each side complements the other's particular weak point rather than matching its pace.

The six pairs: Rat & Ox, Tiger & Pig, Rabbit & Dog, Dragon & Rooster, Snake & Monkey, Horse & Goat. San He is comfort through similarity. Liu He is balance through difference.

Why both appear on the same pages

Any pairing lands in one of four buckets: San He trine, Liu He pair, clash (the six pairs sitting exactly opposite on the wheel, covered in the full compatibility guide), or neutral — the largest bucket by far. Whatever reads as a confident verdict on a compatibility page traces back to one of these four, layered with each sign's individual traits.

Origin

Both predate the "compatibility calculator" framing entirely. They're part of the older, more technical bāzì ("eight characters") tradition used historically by professional fortune-tellers and matchmakers. This site's simplified version strips out the month, day and hour pillars a full bāzì reading would include and keeps only the year-animal relationships — the layer most people mean when they ask about zodiac compatibility at all.

What it isn't for

Not a rulebook for who you're allowed to be close to. Not a predictor of outcomes. It's shared vocabulary for talking about why a relationship feels easy or effortful — most useful as a conversation starter, not a verdict issued before a relationship has had a chance to develop.

Working it out yourself

Know the twelve-animal order — Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig — and count the gap. Four apart, either direction: San He trine. Six apart: clash. Liu He doesn't follow a fixed distance; it's a specific list of six pairs that has to be memorized or looked up, which is why the compatibility section exists as a direct reference rather than a formula.

Why San He groups animals four years apart specifically

The four-year spacing behind San He isn't arbitrary — it splits the twelve-animal wheel into exactly four equal groups of three, the only way to divide twelve animals into equal trios using a single fixed gap. Traditional astrology reads that even spacing as more than geometric convenience: animals sitting at equal distances around the full cycle are treated as moving through the world at a comparable rhythm, even when their surface personalities look nothing alike on paper. A Rat and a Monkey don't resemble each other in temperament the way two signs from the same trine sometimes appear to, but both are quick, opportunistic and comfortable improvising — which is the actual trait the San He grouping is picking up on, once you look past the animals' different reputations.

Why Liu He doesn't follow the same pattern

Where San He is built from pure distance, Liu He is traditionally explained through a lunar-mansion framework — an older Chinese astronomical system that divided the sky into 28 sections used to track the moon's monthly path, each associated with different animals and constellations. The six Liu He pairings are said to derive from which lunar mansions were seen as complementary within that older system, which is why the pairs don't reduce to a clean numeric rule the way San He does. It's a case of one compatibility layer inheriting its logic from geometry (San He) and another inheriting its logic from a much older astronomical framework (Liu He) — two different sources merged together into what today reads as a single compatibility chart.

How the four buckets rank against each other

When a pairing qualifies for more than one category in principle, tradition treats Liu He as the strongest bond available — stronger even than San He — precisely because it's the rarer, more specific relationship (six pairs total, versus San He's four groups of three covering far more combinations). Clash outranks harm in the other direction, as the more serious friction of the two. In practice no animal pair actually qualifies for two categories simultaneously, since the categories are built from non-overlapping year-gaps and fixed lists, but the ranking is still useful to know when comparing how "strong" one match is against another across different pages on this site.

Reading these terms in older or more technical sources

If you come across San He and Liu He in a more academic or historically minded source, they're often introduced alongside their full Chinese terms — 三合 for San He, 六合 for Liu He — and discussed as part of the broader bāzì framework this site's simplified compatibility pages draw from. Older texts sometimes also mention a third, rarer grouping tied to specific day-and-hour pillar combinations rather than the year pillar alone; that layer goes well beyond what a birth-year-only compatibility check like this site's can meaningfully cover, and is generally the domain of a full professional bāzì reading rather than a quick reference page.

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