Stem Combinations and Clashes — the Push and Pull of Heaven's Energy

Just as branches have combinations and clashes with each other, the stems themselves also have combinations and clashes. If branch relationships are ties down on the earth, stem relationships are the push and pull of energy up in the heavens.

Stem Combinations (天干合) come in five pairs — Jia–Ji, Yi–Geng, Bing–Xin, Ding–Ren, Wu–Gui. When two characters join hands, they set aside their original element for a moment and try to turn into a new element (for example, Jia Wood + Ji Earth → Earth). This is called combination-transformation (合化).

The most important point here — Having a combination doesn't automatically mean it turns into a different element. For a combination-transformation to actually take hold, the season (month branch) has to support that element, nothing nearby has to interfere, and the transformed element needs somewhere to root. If the conditions aren't right, the two characters are just just holding onto each other (a combination without the transformation). So be careful about concluding "there's a combination, so this person is definitely like this."

Stem Clashes (天干沖) is a relationship of colliding head-on — Jia–Geng, Yi–Xin, Bing–Ren, Ding–Gui. (The two center Earth stems, Wu and Ji, don't clash.) With a clash present, that energy shakes or collides, and reads as a grain of decisiveness, change, and tension. It isn't bad — read it as a signal of movement and stimulation.