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Thesis
The common mistake is to lift “承一曰台一曰砧以石为之不然以槐桑木半埋地中遣” out of its sentence and turn it into an absolute rule.
Text
“The cheng base, also called tai or zhen, is made of stone; otherwise of locust or mulberry wood, half-buried in the ground so that it will not rock.”
Context
承：垫在规下的台座，又叫台、砧（zhēn）。用石制；或以槐木、桑木半埋入地，使其稳固不摇。
Evidence
- Collation: 各本一致。吴觉农注："半埋地中"是为压实茶饼时台座稳固，唐代制茶作坊的朴拙智慧。
- Existing readings: 吴觉农指出"承"是压制茶饼的操作台，须稳如磐石；"槐、桑木"皆坚重之材，半埋入地以取稳——制茶之讲究，连台座也不放过。
Analysis
The usual misreading extracts “承一曰台一曰砧以石为之不然以槐桑木半埋地中遣” as a slogan. 各本一致。吴觉农注："半埋地中"是为压实茶饼时台座稳固，唐代制茶作坊的朴拙智慧。 In fact every judgment in the chapter carries a limit of place, season and use.
Conclusion
The section does not give a universal rule. It demonstrates a method: read the text, the annotation and the Tang context together before making a modern claim.
Source: The Classic of Tea, Chapter II · The Implements, section 6; the original is in the public domain.
When lost, brew a cup first.