[2156] A phenomenon with an internal object (ajjhattārammaṇo dhammo) is a condition for a phenomenon with an external object (bahiddhārammaṇo dhammo) by decisive-support condition (upanissaya-paccaya): proximity decisive-support (anantarūpanissaya) and natural decisive-support (pakatūpanissaya).
Natural decisive-support: contemplation of impermanence (aniccānupassanā), contemplation of suffering (dukkhānupassanā), and contemplation of impersonality (anattānupassanā) that have an internal object are a condition for contemplation of impermanence, contemplation of suffering, and contemplation of impersonality that have an external object by decisive-support condition.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.