Pattern → formula reasoning
Classical formulas are not symptom-disease lookups. Each formula treats a pattern (zheng) — a constellation of pulse, tongue, and presenting features. Mastery means reading the pattern accurately and recognising when the textbook formula needs structural modification (jia jian).
The Shanghan school
Zhang Zhongjing’s 113 (or 397, depending on edition) formulas are the spine of internal medicine pedagogy. Students memorise the canonical formulas, then study their modifications across two millennia of commentary — Cheng Wuji, Ke Qin, Yu Chang, and the Japanese Kampo tradition.
Modern formula research
Some classical formulas (Gegen Tang, Xiao Chai Hu Tang, Ma Huang Tang) have substantial RCT evidence; others remain experiential. Students learn to assess this gradient honestly, using EBM-Copilot to interrogate the literature for any formula they intend to prescribe.