法界次第初門 1.106

1.106

次十二入而辨十八界者，以惑者迷於名、色俱重故，開色為十，離名作八，合為十八界也。通名界者，以界別為義。此十八法各有別體，義無渾濫，故通受界名也。

Next to the twelve āyatanas, we elucidate the eighteen dhātus because deluded persons are equally confused about both nāma and rūpa; opening form yields ten, and separating nāma makes eight, combining to make the eighteen dhātus. They are universally called "dhātus" (jie) because jie has the meaning of distinct classification. Each of these eighteen dharmas has its distinct essence, and their meanings are never blended or confused; hence they universally receive the name "dhātu."